how to make a person with f-strings

Since I can pass objects into a string with f-strings. I can write one function that makes a person instead of making one function for each person.

preview

I have these tests by the end of the chapter

person/tests/test_person.py
  1import src.person
  2
  3
  4def test_joe():
  5    first_name = 'joe'
  6    last_name = 'blow'
  7    sex = 'M'
  8    year_of_birth = 1996
  9
 10    reality = src.person.factory(
 11        first_name=first_name,
 12        last_name=last_name,
 13        sex=sex,
 14        year_of_birth=year_of_birth,
 15    )
 16    my_expectation = (
 17        f'{first_name}, {last_name},'
 18        f' {sex}, {year_of_birth}'
 19    )
 20    assert reality == my_expectation
 21
 22    reality = src.person.say_hello(
 23        first_name=first_name,
 24        last_name=last_name,
 25        year_of_birth=year_of_birth,
 26    )
 27    my_expectation = (
 28        f'Hello, my name is {first_name}'
 29        f' {last_name} and I am'
 30        f' {2026-year_of_birth}.'
 31    )
 32    assert reality == my_expectation
 33
 34
 35def test_jane():
 36    first_name = 'jane'
 37    last_name = 'doe'
 38    sex = 'F'
 39    year_of_birth = 1991
 40
 41    reality = src.person.factory(
 42        first_name=first_name,
 43        last_name=last_name,
 44        sex=sex,
 45        year_of_birth=year_of_birth,
 46    )
 47    my_expectation = (
 48        f'{first_name}, {last_name},'
 49        f' {sex}, {year_of_birth}'
 50    )
 51    assert reality == my_expectation
 52
 53    reality = src.person.say_hello(
 54        first_name=first_name,
 55        last_name=last_name,
 56        year_of_birth=year_of_birth,
 57    )
 58    my_expectation = (
 59        f'Hello, my name is {first_name}'
 60        f' {last_name} and I am'
 61        f' {2026-year_of_birth}.'
 62    )
 63    assert reality == my_expectation
 64
 65
 66def test_john():
 67    first_name = 'john'
 68    last_name = 'smith'
 69    sex = 'M'
 70    year_of_birth = 1580
 71
 72    reality = src.person.factory(
 73        first_name=first_name,
 74        last_name=last_name,
 75        sex=sex,
 76        year_of_birth=year_of_birth,
 77    )
 78    my_expectation = (
 79        f'{first_name}, {last_name},'
 80        f' {sex}, {year_of_birth}'
 81    )
 82    assert reality == my_expectation
 83
 84    reality = src.person.say_hello(
 85        first_name=first_name,
 86        last_name=last_name,
 87        year_of_birth=year_of_birth,
 88    )
 89    my_expectation = (
 90        f'Hello, my name is {first_name}'
 91        f' {last_name} and I am'
 92        f' {2026-year_of_birth}.'
 93    )
 94    assert reality == my_expectation
 95
 96
 97def test_mary():
 98    first_name = 'mary'
 99    last_name = 'public'
100    sex = 'F'
101    year_of_birth = 2000
102
103    reality = src.person.factory(
104        first_name=first_name,
105        last_name=last_name,
106        sex=sex,
107        year_of_birth=year_of_birth,
108    )
109    my_expectation = (
110        f'{first_name}, {last_name},'
111        f' {sex}, {year_of_birth}'
112    )
113    assert reality == my_expectation
114
115    reality = src.person.say_hello(
116        first_name=first_name,
117        last_name=last_name,
118        year_of_birth=year_of_birth,
119    )
120    my_expectation = (
121        f'Hello, my name is {first_name}'
122        f' {last_name} and I am'
123        f' {2026-year_of_birth}.'
124    )
125    assert reality == my_expectation
126
127
128# Exceptions seen
129# AssertionError
130# NameError
131# TypeError
132# AttributeError

open the project

  • I open a terminal

  • I change directory to the project

    cd person

    the terminal shows I am in the person folder

    .../pumping_python/person

  • I open test_person.py

  • I use pytest-watcher to run the tests automatically

    uv run pytest-watcher . --now

    the terminal shows the tests from before are passing.

test person factory

RED: make it fail

I add an assertion to test_joe in test_person.py

17  def test_joe():
18      assert joe() == 'joe, blow, M, 1996'
19
20      reality = factory()
21      my_expectation = 'joe, blow, M, 1996'
22      assert reality == my_expectation
23
24
25  def test_jane():

the terminal is my friend, and shows NameError

NameError: name 'factory' is not defined

because I have not defined factory in test_person.py, yet.

GREEN: make it pass

I add a function definition for it

1def factory():
2    return 'joe, blow, M, 1996'
3
4
5def joe():

the test passes.

REFACTOR: make it better

  • I add an assertion with a call to the factory function in test_jane

    21def test_joe():
22    assert joe() == 'joe, blow, M, 1996'
23
24    reality = factory()
25    my_expectation = 'joe, blow, M, 1996'
26    assert reality == my_expectation
27
28
29def test_jane():
30    assert jane() == 'jane, doe, F, 1991'
31
32    reality = factory()
33    my_expectation = 'jane, doe, F, 1991'
34    assert reality == my_expectation
35
36
37def test_john():

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'joe, blow, M, 1996'
                    == 'jane, doe, F, 1991'

    because the factory function always returns joe, blow, M, 1996 when it is called. It has to return a string based on the input it gets for me to be able to use it to make more than one person.

  • I make the function take input for the first name

    1# def factory():
2def factory(first_name):
3    return 'joe, blow, M, 1996'

    the terminal is my friend, and shows TypeError

    TypeError: factory() missing
           1 required positional argument:
           'first_name'

    because

  • I add 'jane' to the call to the factory function in test_jane

    30def test_jane():
31    assert jane() == 'jane, doe, F, 1991'
32
33    # reality = factory()
34    reality = factory('jane')
35    my_expectation = 'jane, doe, F, 1991'
36    assert reality == my_expectation
37
38
39def test_john():

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'joe, blow, M, 1996'
                    == 'jane, doe, F, 1991'

  • I change the return statement of the factory function to an f-string to use first_name in the output

    1# def factory():
2def factory(first_name):
3    # return 'joe, blow, M, 1996'
4    return f'{first_name}, blow, M, 1996'
5
6
7def joe():

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'jane, blow, M, 1996'
                    == 'jane, doe, F, 1991'

    the first names match. Progress!

  • I add last_name to the return statement

     1# def factory():
 2def factory(first_name):
 3    # return 'joe, blow, M, 1996'
 4    # return f'{first_name}, blow, M, 1996'
 5    return (
 6        f'{first_name}, {last_name},'
 7        ' M, 1996'
 8    )
 9
10
11def joe():

    the terminal is my friend, and shows NameError

    NameError: name 'last_name' is not defined

  • I add the name to the parentheses to define it in the factory function

     1# def factory():
 2# def factory(first_name):
 3def factory(first_name, last_name):
 4    # return 'joe, blow, M, 1996'
 5    # return f'{first_name}, blow, M, 1996'
 6    return (
 7        f'{first_name}, {last_name},'
 8        ' M, 1996'
 9    )
10
11
12def joe():

    the terminal is my friend, and shows TypeError

    TypeError: factory() missing
           1 required positional argument:
           'last_name'

    because

  • I add 'doe' to the call to the factory function in test_jane

    36def test_jane():
37    assert jane() == 'jane, doe, F, 1991'
38
39    # reality = factory()
40    # reality = factory('jane')
41    reality = factory('jane', 'doe')
42    my_expectation = 'jane, doe, F, 1991'
43    assert reality == my_expectation
44
45
46def test_john():

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'jane, doe, M, 1996'
                    == 'jane, doe, F, 1991'

    the first and last names match. More progress.

  • I change the call to the factory function to use keyword arguments, then add a value for sex (since I have more than two arguments) to in test_jane

    36def test_jane():
37    assert jane() == 'jane, doe, F, 1991'
38
39    # reality = factory()
40    # reality = factory('jane')
41    # reality = factory('jane', 'doe')
42    reality = factory(
43        first_name='jane',
44        last_name='doe',
45        sex='F',
46    )
47    my_expectation = 'jane, doe, F, 1991'
48    assert reality == my_expectation
49
50
51def test_john():

    the terminal is my friend, and shows TypeError

    TypeError: factory() got an unexpected
           keyword argument 'sex'

    because

  • I add sex in the parentheses of the factory function definition

     1# def factory():
 2# def factory(first_name):
 3# def factory(first_name, last_name):
 4def factory(first_name, last_name, sex):
 5    # return 'joe, blow, M, 1996'
 6    # return f'{first_name}, blow, M, 1996'
 7    return (
 8        f'{first_name}, {last_name},'
 9        ' M, 1996'
10    )
11
12
13def joe():

    the terminal shows the last AssertionError again.

  • I add sex to the f-string in the factory function

     1# def factory():
 2# def factory(first_name):
 3# def factory(first_name, last_name):
 4def factory(first_name, last_name, sex):
 5    # return 'joe, blow, M, 1996'
 6    # return f'{first_name}, blow, M, 1996'
 7    return (
 8        f'{first_name}, {last_name},'
 9        # ' M, 1996'
10        f' {sex}, 1996'
11    )
12
13
14def joe():

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'jane, doe, F, 1996'
                    == 'jane, doe, F, 1991'

    the first name, last name and sex match. Yes!

  • I add year_of_birth to the return statement

     1# def factory():
 2# def factory(first_name):
 3# def factory(first_name, last_name):
 4def factory(first_name, last_name, sex):
 5    # return 'joe, blow, M, 1996'
 6    # return f'{first_name}, blow, M, 1996'
 7    return (
 8        f'{first_name}, {last_name},'
 9        # ' M, 1996'
10        # f' {sex}, 1996'
11        f' {sex}, {year_of_birth}'
12    )
13
14
15def joe():

    the terminal is my friend, and shows NameError

    NameError: name 'year_of_birth' is not defined

  • I add year_of_birth to the parentheses to define it in the factory function

     1# def factory():
 2# def factory(first_name):
 3# def factory(first_name, last_name):
 4# def factory(first_name, last_name, sex):
 5def factory(
 6    first_name, last_name,
 7    sex, year_of_birth,
 8):
 9    # return 'joe, blow, M, 1996'
10    # return f'{first_name}, blow, M, 1996'
11    return (
12        f'{first_name}, {last_name},'
13        # ' M, 1996'
14        # f' {sex}, 1996'
15        f' {sex}, {year_of_birth}'
16    )
17
18
19def joe():

    the terminal is my friend, and shows TypeError

    TypeError: factory() missing
           1 required positional argument:
           'year_of_birth'

    because

  • I add year_of_birth=1996 to the call to the factory function in test_jane

    43def test_jane():
44    assert jane() == 'jane, doe, F, 1991'
45
46    # reality = factory()
47    # reality = factory('jane')
48    # reality = factory('jane', 'doe')
49    reality = factory(
50        first_name='jane',
51        last_name='doe',
52        sex='F',
53        year_of_birth=1991,
54    )
55    my_expectation = 'jane, doe, F, 1991'
56    assert reality == my_expectation
57
58
59def test_john():

    the terminal is my friend, and shows TypeError

    TypeError: factory() missing
           4 required positional arguments:
           'first_name', 'last_name', 'sex',
           and 'year_of_birth'

    because

  • Since there are more than two arguments, I add keyword arguments to the call to the factory function in test_joe

    35def test_joe():
36    assert joe() == 'joe, blow, M, 1996'
37
38    # reality = factory()
39    reality = factory(
40        first_name='joe',
41        last_name='blow',
42        sex='M',
43        year_of_birth=1996,
44    )
45    my_expectation = 'joe, blow, M, 1996'
46    assert reality == my_expectation
47
48
49def test_jane():

    the test passes and I have one function that I can use to make any number of people.

  • I remove the commented lines from the factory function

     1def factory(
 2    first_name, last_name,
 3    sex, year_of_birth,
 4):
 5    return (
 6        f'{first_name}, {last_name},'
 7        f' {sex}, {year_of_birth}'
 8    )
 9
10
11def joe():

  • I comment out the call to joe in test_joe because I no longer need it since the factory function does the same thing

    27def test_joe():
28    # assert joe() == 'joe, blow, M, 1996'
29
30    reality = factory(
31        first_name='joe',
32        last_name='blow',
33        sex='M',
34        year_of_birth=1996,
35    )
36    my_expectation = 'joe, blow, M, 1996'
37    assert reality == my_expectation
38
39
40def test_jane():

  • I add a variable for 'joe' in test_joe

    27def test_joe():
28    # assert joe() == 'joe, blow, M, 1996'
29    first_name = 'joe'
30
31    reality = factory(
32        first_name='joe',
33        last_name='blow',
34        sex='M',
35        year_of_birth=1996,
36    )
37    my_expectation = 'joe, blow, M, 1996'
38    assert reality == my_expectation
39
40
41def test_jane():

  • I use the variable to remove repetition of 'joe'

    27def test_joe():
28    # assert joe() == 'joe, blow, M, 1996'
29    first_name = 'joe'
30
31    reality = factory(
32        # first_name='joe',
33        first_name=first_name,
34        last_name='blow',
35        sex='M',
36        year_of_birth=1996,
37    )
38    # my_expectation = 'joe, blow, M, 1996'
39    my_expectation = (
40        f'{first_name}, blow,'
41        ' M, 1996'
42    )
43    assert reality == my_expectation
44
45
46def test_jane():

    the test is still green.

  • I add a variable for 'blow' in test_joe

    27def test_joe():
28    # assert joe() == 'joe, blow, M, 1996'
29    first_name = 'joe'
30    last_name = 'blow'
31
32    reality = factory(
33        # first_name='joe',
34        first_name=first_name,
35        last_name='blow',
36        sex='M',
37        year_of_birth=1996,
38    )
39    # my_expectation = 'joe, blow, M, 1996'
40    my_expectation = (
41        f'{first_name}, blow,'
42        ' M, 1996'
43    )
44    assert reality == my_expectation
45
46
47def test_jane():

  • I use the variable to remove repetition of 'blow'

    27def test_joe():
28    # assert joe() == 'joe, blow, M, 1996'
29    first_name = 'joe'
30    last_name = 'blow'
31
32    reality = factory(
33        # first_name='joe',
34        first_name=first_name,
35        # last_name='blow',
36        last_name=last_name,
37        sex='M',
38        year_of_birth=1996,
39    )
40    # my_expectation = 'joe, blow, M, 1996'
41    my_expectation = (
42        # f'{first_name}, blow,'
43        f'{first_name}, {last_name},'
44        ' M, 1996'
45    )
46    assert reality == my_expectation
47
48
49def test_jane():

    still green.

  • I add a variable for 'M' in test_joe

    27def test_joe():
28    # assert joe() == 'joe, blow, M, 1996'
29    first_name = 'joe'
30    last_name = 'blow'
31    sex = 'M'
32
33    reality = factory(
34        # first_name='joe',
35        first_name=first_name,
36        # last_name='blow',
37        last_name=last_name,
38        sex='M',
39        year_of_birth=1996,
40    )

  • I use the variable to remove repetition of 'M'

    27def test_joe():
28    # assert joe() == 'joe, blow, M, 1996'
29    first_name = 'joe'
30    last_name = 'blow'
31    sex = 'M'
32
33    reality = factory(
34        # first_name='joe',
35        first_name=first_name,
36        # last_name='blow',
37        last_name=last_name,
38        # sex='M',
39        sex=sex,
40        year_of_birth=1996,
41    )
42    # my_expectation = 'joe, blow, M, 1996'
43    my_expectation = (
44        # f'{first_name}, blow,'
45        f'{first_name}, {last_name},'
46        # ' M, 1996'
47        f' {sex}, 1996'
48    )
49    assert reality == my_expectation
50
51
52def test_jane():

    green.

  • I add a variable for 1996 in test_joe

    27def test_joe():
28    # assert joe() == 'joe, blow, M, 1996'
29    first_name = 'joe'
30    last_name = 'blow'
31    sex = 'M'
32    year_of_birth = 1996
33
34    reality = factory(
35        # first_name='joe',
36        first_name=first_name,
37        # last_name='blow',
38        last_name=last_name,
39        # sex='M',
40        sex=sex,
41        year_of_birth=1996,
42    )

  • I use the variable to remove repetition of 1996

    27def test_joe():
28    # assert joe() == 'joe, blow, M, 1996'
29    first_name = 'joe'
30    last_name = 'blow'
31    sex = 'M'
32    year_of_birth = 1996
33
34    reality = factory(
35        # first_name='joe',
36        first_name=first_name,
37        # last_name='blow',
38        last_name=last_name,
39        # sex='M',
40        sex=sex,
41        # year_of_birth=1996,
42        year_of_birth=year_of_birth,
43    )
44    # my_expectation = 'joe, blow, M, 1996'
45    my_expectation = (
46        # f'{first_name}, blow,'
47        f'{first_name}, {last_name},'
48        # ' M, 1996'
49        # f' {sex}, 1996'
50        f' {sex}, {year_of_birth}'
51    )
52    assert reality == my_expectation
53
54
55def test_jane():

    still green.

  • I remove the commented lines

    27def test_joe():
28    first_name = 'joe'
29    last_name = 'blow'
30    sex = 'M'
31    year_of_birth = 1996
32
33    reality = factory(
34        first_name=first_name,
35        last_name=last_name,
36        sex=sex,
37        year_of_birth=year_of_birth,
38    )
39    my_expectation = (
40        f'{first_name}, {last_name},'
41        f' {sex}, {year_of_birth}'
42    )
43    assert reality == my_expectation
44
45
46def test_jane():

  • I comment out the call to jane in test_jane because I no longer need it since the factory function does the same thing

    46def test_jane():
47    # assert jane() == 'jane, doe, F, 1991'
48
49    # reality = factory()

  • I add a variable for 'jane' in test_jane

    46def test_jane():
47    # assert jane() == 'jane, doe, F, 1991'
48    first_name = 'jane'
49
50    # reality = factory()

  • I use the variable to remove repetition of 'jane'

    46def test_jane():
47    # assert jane() == 'jane, doe, F, 1991'
48    first_name = 'jane'
49
50    # reality = factory()
51    # reality = factory('jane')
52    # reality = factory('jane', 'doe')
53    reality = factory(
54        # first_name='jane',
55        first_name=first_name,
56        last_name='doe',
57        sex='F',
58        year_of_birth=1991,
59    )
60    # my_expectation = 'jane, doe, F, 1991'
61    my_expectation = (
62        f'{first_name}, doe,'
63        ' F, 1991'
64    )
65    assert reality == my_expectation
66
67
68def test_john():

    the test is still green.

  • I add a variable for 'doe' in test_jane

    46def test_jane():
47    # assert jane() == 'jane, doe, F, 1991'
48    first_name = 'jane'
49    last_name = 'doe'
50
51    # reality = factory()

  • I use the variable to remove repetition of 'doe'

    46def test_jane():
47    # assert jane() == 'jane, doe, F, 1991'
48    first_name = 'jane'
49    last_name = 'doe'
50
51    # reality = factory()
52    # reality = factory('jane')
53    # reality = factory('jane', 'doe')
54    reality = factory(
55        # first_name='jane',
56        first_name=first_name,
57        # last_name='doe',
58        last_name=last_name,
59        sex='F',
60        year_of_birth=1991,
61    )
62    # my_expectation = 'jane, doe, F, 1991'
63    my_expectation = (
64        # f'{first_name}, doe,'
65        f'{first_name}, {last_name},'
66        ' F, 1991'
67    )
68    assert reality == my_expectation
69
70
71def test_john():

    still green.

  • I add a variable for 'F' in test_jane

    46def test_jane():
47    # assert jane() == 'jane, doe, F, 1991'
48    first_name = 'jane'
49    last_name = 'doe'
50    sex = 'F'
51
52    # reality = factory()

  • I use the variable to remove repetition of 'F'

    46def test_jane():
47    # assert jane() == 'jane, doe, F, 1991'
48    first_name = 'jane'
49    last_name = 'doe'
50    sex = 'F'
51
52    # reality = factory()
53    # reality = factory('jane')
54    # reality = factory('jane', 'doe')
55    reality = factory(
56        # first_name='jane',
57        first_name=first_name,
58        # last_name='doe',
59        last_name=last_name,
60        # sex='F',
61        sex=sex,
62        year_of_birth=1991,
63    )
64    # my_expectation = 'jane, doe, F, 1991'
65    my_expectation = (
66        # f'{first_name}, doe,'
67        f'{first_name}, {last_name},'
68        # ' F, 1991'
69        f' {sex}, 1991'
70    )
71    assert reality == my_expectation
72
73
74def test_john():

    green.

  • I add a variable for 1991 in test_jane

    46def test_jane():
47    # assert jane() == 'jane, doe, F, 1991'
48    first_name = 'jane'
49    last_name = 'doe'
50    sex = 'F'
51    year_of_birth = 1991
52
53    # reality = factory()

  • I use the variable to remove repetition of 1991

    46def test_jane():
47    # assert jane() == 'jane, doe, F, 1991'
48    first_name = 'jane'
49    last_name = 'doe'
50    sex = 'F'
51    year_of_birth = 1991
52
53    # reality = factory()
54    # reality = factory('jane')
55    # reality = factory('jane', 'doe')
56    reality = factory(
57        # first_name='jane',
58        first_name=first_name,
59        # last_name='doe',
60        last_name=last_name,
61        # sex='F',
62        sex=sex,
63        # year_of_birth=1991,
64        year_of_birth=year_of_birth,
65    )
66    # my_expectation = 'jane, doe, F, 1991'
67    my_expectation = (
68        # f'{first_name}, doe,'
69        f'{first_name}, {last_name},'
70        # ' F, 1991'
71        # f' {sex}, 1991'
72        f' {sex}, {year_of_birth}'
73    )
74    assert reality == my_expectation
75
76
77def test_john():

    still green.

  • I remove the commented lines

    46def test_jane():
47    first_name = 'jane'
48    last_name = 'doe'
49    sex = 'F'
50    year_of_birth = 1991
51
52    reality = factory(
53        first_name=first_name,
54        last_name=last_name,
55        sex=sex,
56        year_of_birth=year_of_birth,
57    )
58    my_expectation = (
59        f'{first_name}, {last_name},'
60        f' {sex}, {year_of_birth}'
61    )
62    assert reality == my_expectation
63
64
65def test_john():

  • I change the call in test_john to a call to the factory function

    65def test_john():
66    # assert john() == 'john, smith, M, 1580'
67    reality = factory(
68        first_name='john',
69        last_name='smith',
70        sex='M',
71        year_of_birth=1580,
72    )
73    my_expectation = 'jane, doe, F, 1991'
74    assert reality == my_expectation
75
76
77def test_mary():

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'john, smith, M, 1580'
                    == 'jane, doe, F, 1991'

  • I change my_expectation to match reality

    65def test_john():
66    # assert john() == 'john, smith, M, 1580'
67    reality = factory(
68        first_name='john',
69        last_name='smith',
70        sex='M',
71        year_of_birth=1580,
72    )
73    # my_expectation = 'jane, doe, F, 1991'
74    my_expectation = 'john, smith, M, 1580'
75    assert reality == my_expectation
76
77
78def test_mary():

    the test passes.

  • I add a variable for 'john' in test_john

    65def test_john():
66    # assert john() == 'john, smith, M, 1580'
67    first_name = 'john'
68
69    reality = factory(
70        first_name='john',
71        last_name='smith',
72        sex='M',
73        year_of_birth=1580,
74    )
75    # my_expectation = 'jane, doe, F, 1991'
76    my_expectation = 'john, smith, M, 1580'
77    assert reality == my_expectation
78
79
80def test_mary():

  • I use the variable to remove repetition of 'john'

    65def test_john():
66    # assert john() == 'john, smith, M, 1580'
67    first_name = 'john'
68
69    reality = factory(
70        # first_name='john',
71        first_name=first_name,
72        last_name='smith',
73        sex='M',
74        year_of_birth=1580,
75    )
76    # my_expectation = 'jane, doe, F, 1991'
77    # my_expectation = 'john, smith, M, 1580'
78    my_expectation = (
79        f'{first_name}, smith,'
80        ' M, 1580'
81    )
82    assert reality == my_expectation
83
84
85def test_mary():

    the test is still green.

  • I add a variable for 'smith' in test_john

    65def test_john():
66    # assert john() == 'john, smith, M, 1580'
67    first_name = 'john'
68    last_name = 'smith'

  • I use the variable to remove repetition of 'smith'

    65def test_john():
66    # assert john() == 'john, smith, M, 1580'
67    first_name = 'john'
68    last_name = 'smith'
69
70    reality = factory(
71        # first_name='john',
72        first_name=first_name,
73        # last_name='smith',
74        last_name=last_name,
75        sex='M',
76        year_of_birth=1580,
77    )
78    # my_expectation = 'jane, doe, F, 1991'
79    # my_expectation = 'john, smith, M, 1580'
80    my_expectation = (
81        # f'{first_name}, smith,'
82        f'{first_name}, {last_name},'
83        ' M, 1580'
84    )
85    assert reality == my_expectation
86
87
88def test_mary():

    still green.

  • I add a variable for 'M' in test_john

    65def test_john():
66    # assert john() == 'john, smith, M, 1580'
67    first_name = 'john'
68    last_name = 'smith'
69    sex = 'M'

  • I use the variable to remove repetition of 'M'

    65def test_john():
66    # assert john() == 'john, smith, M, 1580'
67    first_name = 'john'
68    last_name = 'smith'
69    sex = 'M'
70
71    reality = factory(
72        # first_name='john',
73        first_name=first_name,
74        # last_name='smith',
75        last_name=last_name,
76        # sex='M',
77        sex=sex,
78        year_of_birth=1580,
79    )
80    # my_expectation = 'jane, doe, F, 1991'
81    # my_expectation = 'john, smith, M, 1580'
82    my_expectation = (
83        # f'{first_name}, smith,'
84        f'{first_name}, {last_name},'
85        # ' M, 1580'
86        f' {sex}, 1580'
87    )
88    assert reality == my_expectation
89
90
91def test_mary():

    green.

  • I add a variable for 1580 in test_john

    65def test_john():
66    # assert john() == 'john, smith, M, 1580'
67    first_name = 'john'
68    last_name = 'smith'
69    sex = 'M'
70    year_of_birth = 1580

  • I use the variable to remove repetition of 1580

    65def test_john():
66    # assert john() == 'john, smith, M, 1580'
67    first_name = 'john'
68    last_name = 'smith'
69    sex = 'M'
70    year_of_birth = 1580
71
72    reality = factory(
73        # first_name='john',
74        first_name=first_name,
75        # last_name='smith',
76        last_name=last_name,
77        # sex='M',
78        sex=sex,
79        # year_of_birth=1580,
80        year_of_birth=year_of_birth,
81    )
82    # my_expectation = 'jane, doe, F, 1991'
83    # my_expectation = 'john, smith, M, 1580'
84    my_expectation = (
85        # f'{first_name}, smith,'
86        f'{first_name}, {last_name},'
87        # ' M, 1580'
88        # f' {sex}, 1580'
89        f' {sex}, {year_of_birth}'
90    )
91    assert reality == my_expectation
92
93
94def test_mary():

    still green.

  • I remove the commented lines

    65def test_john():
66    first_name = 'john'
67    last_name = 'smith'
68    sex = 'M'
69    year_of_birth = 1580
70
71    reality = factory(
72        first_name=first_name,
73        last_name=last_name,
74        sex=sex,
75        year_of_birth=year_of_birth,
76    )
77    my_expectation = (
78        f'{first_name}, {last_name},'
79        f' {sex}, {year_of_birth}'
80    )
81    assert reality == my_expectation
82
83
84def test_mary():

  • I make the same change to test_mary

     84def test_mary():
 85    # assert mary() == 'mary, public, F, 2000'
 86    first_name = 'mary'
 87    last_name = 'public'
 88    sex = 'F'
 89    year_of_birth = 2000
 90
 91    reality = factory(
 92        first_name=first_name,
 93        last_name=last_name,
 94        sex=sex,
 95        year_of_birth=year_of_birth,
 96    )
 97    my_expectation = (
 98        f'{first_name}, {last_name},'
 99        f' {sex}, {year_of_birth}'
100    )
101    assert reality == my_expectation
102
103
104# Exceptions seen

    the test is still green.

  • I remove the commented line

     84def test_mary():
 85    first_name = 'mary'
 86    last_name = 'public'
 87    sex = 'F'
 88    year_of_birth = 2000
 89
 90    reality = factory(
 91        first_name=first_name,
 92        last_name=last_name,
 93        sex=sex,
 94        year_of_birth=year_of_birth,
 95    )
 96    my_expectation = (
 97        f'{first_name}, {last_name},'
 98        f' {sex}, {year_of_birth}'
 99    )
100    assert reality == my_expectation
101
102
103# Exceptions seen

  • I remove the joe, jane, john and mary functions because they are no longer used

     1def factory(
 2    first_name, last_name,
 3    sex, year_of_birth,
 4):
 5    return (
 6        f'{first_name}, {last_name},'
 7        f' {sex}, {year_of_birth}'
 8    )
 9
10
11def test_joe():

    the factory function can make a string for any person I want when I give it the first name, last name, sex and year of birth.

  • I open a new terminal then change directories to person

    cd person

  • I add a git commit message in the new terminal

    git commit -am 'extract factory function'

RED: make it fail

  • I go back to the terminal where the tests are running

  • I change reality for test_joe to be the result of a call to the factory function of the person module in the src folder instead of a call to the factory function in test_person.py

    11def test_joe():
12    first_name = 'joe'
13    last_name = 'blow'
14    sex = 'M'
15    year_of_birth = 1996
16
17    # reality = factory(
18    reality = src.person.factory(
19        first_name=first_name,
20        last_name=last_name,
21        sex=sex,
22        year_of_birth=year_of_birth,
23    )
24    my_expectation = (
25        f'{first_name}, {last_name},'
26        f' {sex}, {year_of_birth}'
27    )
28    assert reality == my_expectation
29
30
31def test_jane():

    the terminal is my friend, and shows NameError

    NameError: name 'src' is not defined

    because src is not defined in test_person.py

GREEN: make it pass

  • I add an import statement at the top of test_person.py

    1import src.person
2
3
4def factory(
5    first_name, last_name,
6    sex, year_of_birth,
7):

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.person' has no attribute 'factory'

    because there is nothing named factory in person.py in the src folder.

  • I add AttributeError to the list of Exceptions seen

    90# Exceptions seen
91# AssertionError
92# NameError
93# TypeError
94# AttributeError

  • I open person/__init__.py from the src folder

  • I delete all the text in the file then add a copy of the factory function to person.py

    1def factory(
2    first_name, last_name,
3    sex, year_of_birth,
4):
5    return (
6        f'{first_name}, {last_name},'
7        f' {sex}, {year_of_birth}'
8    )

    the test passes because

    • Python brings in an object for the person.py file from the src folder so I can use it in test_person.py as src.person when import src.person runs.

    • Python calls the factory function from the object it imported for the person.py file from the src folder (src.person) when src.person.factory is called.

    I think of src.person.factory like an address

    • factory is something in person, in this case it is a function in person

    • person is something in src, in this case it is person.py (a module) in the src folder

    • src is something Python can import (a module, Python package or folder)

      src.person.factory
src
└── person.py
    └── def factory(
            first_name, last_name,
            sex, year_of_birth,
        ):
        └── return (
                f'{first_name}, {last_name},'
                f' {sex}, {year_of_birth}'
            )

REFACTOR: make it better

  • I remove the commented line from test_joe in test_person.py

    14def test_joe():
15    first_name = 'joe'
16    last_name = 'blow'
17    sex = 'M'
18    year_of_birth = 1996
19
20    reality = src.person.factory(
21        first_name=first_name,
22        last_name=last_name,
23        sex=sex,
24        year_of_birth=year_of_birth,
25    )
26    my_expectation = (
27        f'{first_name}, {last_name},'
28        f' {sex}, {year_of_birth}'
29    )
30    assert reality == my_expectation
31
32
33def test_jane():

  • I change reality for test_jane to be the result of a call to the factory function of the person module in the src folder

    33def test_jane():
34    first_name = 'jane'
35    last_name = 'doe'
36    sex = 'F'
37    year_of_birth = 1991
38
39    # reality = factory(
40    reality = src.person.factory(
41        first_name=first_name,
42        last_name=last_name,
43        sex=sex,
44        year_of_birth=year_of_birth,
45    )
46    my_expectation = (
47        f'{first_name}, {last_name},'
48        f' {sex}, {year_of_birth}'
49    )
50    assert reality == my_expectation
51
52
53def test_john():

    the test is still green.

  • I remove the commented line from test_jane

    33def test_jane():
34    first_name = 'jane'
35    last_name = 'doe'
36    sex = 'F'
37    year_of_birth = 1991
38
39    reality = src.person.factory(
40        first_name=first_name,
41        last_name=last_name,
42        sex=sex,
43        year_of_birth=year_of_birth,
44    )
45    my_expectation = (
46        f'{first_name}, {last_name},'
47        f' {sex}, {year_of_birth}'
48    )
49    assert reality == my_expectation
50
51
52def test_john():

  • I change reality for test_john to be the result of a call to the factory function of the person module in the src folder

    52def test_john():
53    first_name = 'john'
54    last_name = 'smith'
55    sex = 'M'
56    year_of_birth = 1580
57
58    # reality = factory(
59    reality = src.person.factory(
60        first_name=first_name,
61        last_name=last_name,
62        sex=sex,
63        year_of_birth=year_of_birth,
64    )
65    my_expectation = (
66        f'{first_name}, {last_name},'
67        f' {sex}, {year_of_birth}'
68    )
69    assert reality == my_expectation
70
71
72def test_mary():

    still green.

  • I remove the commented line

    52def test_john():
53    first_name = 'john'
54    last_name = 'smith'
55    sex = 'M'
56    year_of_birth = 1580
57
58    reality = src.person.factory(
59        first_name=first_name,
60        last_name=last_name,
61        sex=sex,
62        year_of_birth=year_of_birth,
63    )
64    my_expectation = (
65        f'{first_name}, {last_name},'
66        f' {sex}, {year_of_birth}'
67    )
68    assert reality == my_expectation
69
70
71def test_mary():

  • I do the same thing to the call to the factory function in test_mary

    71def test_mary():
72    first_name = 'mary'
73    last_name = 'public'
74    sex = 'F'
75    year_of_birth = 2000
76
77    # reality = factory(
78    reality = src.person.factory(
79        first_name=first_name,
80        last_name=last_name,
81        sex=sex,
82        year_of_birth=year_of_birth,
83    )
84    my_expectation = (
85        f'{first_name}, {last_name},'
86        f' {sex}, {year_of_birth}'
87    )
88    assert reality == my_expectation
89
90
91# Exceptions seen

    green.

  • I remove the commented line

    71def test_mary():
72    first_name = 'mary'
73    last_name = 'public'
74    sex = 'F'
75    year_of_birth = 2000
76
77    reality = src.person.factory(
78        first_name=first_name,
79        last_name=last_name,
80        sex=sex,
81        year_of_birth=year_of_birth,
82    )
83    my_expectation = (
84        f'{first_name}, {last_name},'
85        f' {sex}, {year_of_birth}'
86    )
87    assert reality == my_expectation
88
89
90# Exceptions seen
91# AssertionError
92# NameError
93# TypeError
94# AttributeError

  • I remove the factory function from test_person.py

     1import src.person
 2
 3
 4def test_joe():
 5    first_name = 'joe'
 6    last_name = 'blow'
 7    sex = 'M'
 8    year_of_birth = 1996
 9
10    reality = src.person.factory(
11        first_name=first_name,
12        last_name=last_name,
13        sex=sex,
14        year_of_birth=year_of_birth,
15    )
16    my_expectation = (
17        f'{first_name}, {last_name},'
18        f' {sex}, {year_of_birth}'
19    )
20    assert reality == my_expectation
21
22
23def test_jane():

    all the tests are still green because the calls that were made to the factory function that was in test_person.py are now made to the factory function in person.py in the src folder. When src.person.factory is called, Python follows this path

    src.person.factory
src
└── person.py
    └── def factory(
            first_name, last_name,
            sex, year_of_birth,
        ):
        └── return (
                f'{first_name}, {last_name},'
                f' {sex}, {year_of_birth}'
            )

  • I add a git commit message in the other terminal

    git commit -am \
'move factory function to person.py'

    the terminal shows a summary of the changes then goes back to the command line.

I can write solutions in a different module from the tests.

test say_hello function

I want the person I make to say hi. I can make a function that takes input about a person and returns a message.

RED: make it fail

  • I add an assertion to test_joe in test_person.py

     1import src.person
 2
 3
 4def test_joe():
 5    first_name = 'joe'
 6    last_name = 'blow'
 7    sex = 'M'
 8    year_of_birth = 1996
 9
10    reality = src.person.factory(
11        first_name=first_name,
12        last_name=last_name,
13        sex=sex,
14        year_of_birth=year_of_birth,
15    )
16    my_expectation = (
17        f'{first_name}, {last_name},'
18        f' {sex}, {year_of_birth}'
19    )
20    assert reality == my_expectation
21
22    reality = say_hello(
23        first_name=first_name,
24        last_name=last_name,
25        year_of_birth=year_of_birth,
26    )
27    my_expectation = (
28        f'Hello, my name is {first_name}'
29        f' {last_name} and I am'
30        f' {2026-year_of_birth}.'
31    )
32    assert reality == my_expectation
33
34
35def test_jane():

    the terminal is my friend, and shows NameError

    NameError: name 'say_hello' is not defined

GREEN: make it pass

  • I add a function definition for it

    1import src.person
2
3
4def say_hello():
5    return None
6
7
8def test_joe():

    the terminal is my friend, and shows TypeError

    TypeError: say_hello() got an
           unexpected keyword argument
           'first_name'

    because

  • I add first_name in parentheses

    4# def say_hello():
5def say_hello(first_name):
6    return None
7
8
9def test_joe():

    the terminal is my friend, and shows TypeError

    TypeError: say_hello()
           got an unexpected keyword argument 'last_name'.
           Did you mean 'first_name'?

  • I add last_name in parentheses

     4# def say_hello():
 5# def say_hello(first_name):
 6def say_hello(first_name, last_name):
 7    return None
 8
 9
10def test_joe():

    the terminal is my friend, and shows TypeError

    TypeError: say_hello()
           got an unexpected keyword argument
           'year_of_birth'

    because

  • I add year_of_birth in parentheses

     4# def say_hello():
 5# def say_hello(first_name):
 6# def say_hello(first_name, last_name):
 7def say_hello(
 8    first_name, last_name,
 9    year_of_birth
10):
11    return None
12
13
14def test_joe():

    the terminal is my friend, and shows AssertionError

    AssertionError: assert None
    == 'Hello, my name is joe blow and I am 30.'

  • I change the return statement to give the test what it wants

     4# def say_hello():
 5# def say_hello(first_name):
 6# def say_hello(first_name, last_name):
 7def say_hello(
 8    first_name, last_name,
 9    year_of_birth
10):
11    # return None
12    return 'Hello, my name is joe blow and I am 30.'
13
14
15def test_joe():

    the test passes.

REFACTOR: make it better

  • I add an assertion for the say_hello function to test_jane in test_person.py

    46def test_jane():
47    first_name = 'jane'
48    last_name = 'doe'
49    sex = 'F'
50    year_of_birth = 1991
51
52    reality = src.person.factory(
53        first_name=first_name,
54        last_name=last_name,
55        sex=sex,
56        year_of_birth=year_of_birth,
57    )
58    my_expectation = (
59        f'{first_name}, {last_name},'
60        f' {sex}, {year_of_birth}'
61    )
62    assert reality == my_expectation
63
64    reality = say_hello(
65        first_name=first_name,
66        last_name=last_name,
67        year_of_birth=year_of_birth,
68    )
69    my_expectation = (
70        f'Hello, my name is {first_name}'
71        f' {last_name} and I am'
72        f' {2026-year_of_birth}.'
73    )
74    assert reality == my_expectation
75
76
77def test_john():

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'Hello, my name ... and I am 30.'
                    == 'Hello, my name ... and I am 35.'

  • I change the return statement of the say_hello function to an f-string to use first_name in the output

     4# def say_hello():
 5# def say_hello(first_name):
 6# def say_hello(first_name, last_name):
 7def say_hello(
 8    first_name, last_name,
 9    year_of_birth
10):
11    # return None
12    # return 'Hello, my name is joe blow and I am 30.'
13    return (
14        f'Hello, my name is {first_name}'
15        ' blow and I am 30.'
16    )
17
18
19def test_joe():

    the terminal shows AssertionError

    AssertionError: assert 'Hello, my name ... and I am 30.'
                    == 'Hello, my name ... and I am 35.'

    the first names now match and I still need better error messages.

  • I add last_name to the return statement

     4# def say_hello():
 5# def say_hello(first_name):
 6# def say_hello(first_name, last_name):
 7def say_hello(
 8    first_name, last_name,
 9    year_of_birth
10):
11    # return None
12    # return 'Hello, my name is joe blow and I am 30.'
13    return (
14        f'Hello, my name is {first_name}'
15        # ' blow and I am 30.'
16        f' {last_name} and I am 30.'
17    )
18
19
20def test_joe():

    the terminal shows AssertionError

    AssertionError: assert 'Hello, my name ... and I am 30.'
                    == 'Hello, my name ... and I am 35.'

    the ages are different.

  • I add the age calculation to the return statement

     4# def say_hello():
 5# def say_hello(first_name):
 6# def say_hello(first_name, last_name):
 7def say_hello(
 8    first_name, last_name,
 9    year_of_birth
10):
11    # return None
12    # return 'Hello, my name is joe blow and I am 30.'
13    age = 2026 - year_of_birth
14
15    return (
16        f'Hello, my name is {first_name}'
17        # ' blow and I am 30.'
18        # f' {last_name} and I am 30.'
19        f' {last_name} and I am {age}.'
20    )
21
22
23def test_joe():

    the test passes.

  • I add an assertion for the say_hello function to test_john in test_person.py

     85def test_john():
 86    first_name = 'john'
 87    last_name = 'smith'
 88    sex = 'M'
 89    year_of_birth = 1580
 90
 91    reality = src.person.factory(
 92        first_name=first_name,
 93        last_name=last_name,
 94        sex=sex,
 95        year_of_birth=year_of_birth,
 96    )
 97    my_expectation = (
 98        f'{first_name}, {last_name},'
 99        f' {sex}, {year_of_birth}'
100    )
101    assert reality == my_expectation
102
103    reality = say_hello(
104        first_name=first_name,
105        last_name=last_name,
106        year_of_birth=year_of_birth,
107    )
108    my_expectation = (
109        'Hello, my name is jane'
110        f' {last_name} and I am'
111        f' {2026-year_of_birth}.'
112    )
113    assert reality == my_expectation
114
115
116def test_mary():

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'Hello, my name ...and I am 446.'
                    == 'Hello, my name ...and I am 446.'

  • I change my_expectation to match reality in test_john

    103    reality = say_hello(
104        first_name=first_name,
105        last_name=last_name,
106        year_of_birth=year_of_birth,
107    )
108    my_expectation = (
109        # 'Hello, my name is jane'
110        f'Hello, my name is {first_name}'
111        f' {last_name} and I am'
112        f' {2026-year_of_birth}.'
113    )
114    assert reality == my_expectation
115
116
117def test_mary():

    the test passes.

  • I add an assertion for the say_hello function to test_mary

    117def test_mary():
118    first_name = 'mary'
119    last_name = 'public'
120    sex = 'F'
121    year_of_birth = 2000
122
123    reality = src.person.factory(
124        first_name=first_name,
125        last_name=last_name,
126        sex=sex,
127        year_of_birth=year_of_birth,
128    )
129    my_expectation = (
130        f'{first_name}, {last_name},'
131        f' {sex}, {year_of_birth}'
132    )
133    assert reality == my_expectation
134
135    reality = say_hello(
136        first_name=first_name,
137        last_name=last_name,
138        year_of_birth=year_of_birth,
139    )
140    my_expectation = (
141        f'Hello, my name is {first_name}'
142        ' smith and I am'
143        f' {2026-year_of_birth}.'
144    )
145    assert reality == my_expectation
146
147
148# Exceptions seen

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'Hello, my name ... and I am 26.'
                    == 'Hello, my name ... and I am 26.'

    • The last names are different.

    • I want better messages that show as much of the difference in the summary.

  • I change my_expectation to match reality in test_mary

    135    reality = say_hello(
136        first_name=first_name,
137        last_name=last_name,
138        year_of_birth=year_of_birth,
139    )
140    my_expectation = (
141        f'Hello, my name is {first_name}'
142        # ' smith and I am'
143        f' {last_name} and I am'
144        f' {2026-year_of_birth}.'
145    )
146    assert reality == my_expectation
147
148
149# Exceptions seen

    the test passes.

  • I remove the commented line

    116def test_mary():
117    first_name = 'mary'
118    last_name = 'public'
119    sex = 'F'
120    year_of_birth = 2000
121
122    reality = src.person.factory(
123        first_name=first_name,
124        last_name=last_name,
125        sex=sex,
126        year_of_birth=year_of_birth,
127    )
128    my_expectation = (
129        f'{first_name}, {last_name},'
130        f' {sex}, {year_of_birth}'
131    )
132    assert reality == my_expectation
133
134    reality = say_hello(
135        first_name=first_name,
136        last_name=last_name,
137        year_of_birth=year_of_birth,
138    )
139    my_expectation = (
140        f'Hello, my name is {first_name}'
141        f' {last_name} and I am'
142        f' {2026-year_of_birth}.'
143    )
144    assert reality == my_expectation
145
146
147# Exceptions seen

    the test passes because Python uses the string representation of the object in the curly braces { }

    say_hello(
    first_name=first_name,
    last_name=last_name,
    year_of_birth=year_of_birth,
)
    say_hello(
        first_name, last_name,
        year_of_birth,
    )
        first_name = 'mary'
        last_name = 'public'
        year_of_birth = 1991

        age = 2026 - year_of_birth
        age = 2026 - 1991
        age = 35

        return (
            f'Hello, my name is {first_name}'
            f' {last_name} and I am {age}.'
        )
        return f'Hello, my name is mary public and I am 35'

separate and equal say_hello

  • I change reality to be the result of a call to the say_hello function of the person module in the src folder instead of a call to the say_hello function in test_person.py

    117def test_mary():
118    first_name = 'mary'
119    last_name = 'public'
120    sex = 'F'
121    year_of_birth = 2000
122
123    reality = src.person.factory(
124        first_name=first_name,
125        last_name=last_name,
126        sex=sex,
127        year_of_birth=year_of_birth,
128    )
129    my_expectation = (
130        f'{first_name}, {last_name},'
131        f' {sex}, {year_of_birth}'
132    )
133    assert reality == my_expectation
134
135    # reality = say_hello(
136    reality = src.person.say_hello(
137        first_name=first_name,
138        last_name=last_name,
139        year_of_birth=year_of_birth,
140    )
141    my_expectation = (
142        f'Hello, my name is {first_name}'
143        # ' smith and I am'
144        f' {last_name} and I am'
145        f' {2026-year_of_birth}.'
146    )
147    assert reality == my_expectation
148
149
150# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.person'
                has no attribute 'say_hello'

    because there is nothing named say_hello in the person.py file in the src folder.

  • I add a copy of the say_hello function without the commented lines to person.py

     1def factory(
 2    first_name, last_name,
 3    sex, year_of_birth,
 4):
 5    return (
 6        f'{first_name}, {last_name},'
 7        f' {sex}, {year_of_birth}'
 8    )
 9
10
11def say_hello(
12    first_name, last_name,
13    year_of_birth
14):
15    age = 2026 - year_of_birth
16
17    return (
18        f'Hello, my name is {first_name}'
19        f' {last_name} and I am {age}.'
20    )

    the test passes.

  • I remove the commented lines from test_mary in test_person.py

    117def test_mary():
118    first_name = 'mary'
119    last_name = 'public'
120    sex = 'F'
121    year_of_birth = 2000
122
123    reality = src.person.factory(
124        first_name=first_name,
125        last_name=last_name,
126        sex=sex,
127        year_of_birth=year_of_birth,
128    )
129    my_expectation = (
130        f'{first_name}, {last_name},'
131        f' {sex}, {year_of_birth}'
132    )
133    assert reality == my_expectation
134
135    reality = src.person.say_hello(
136        first_name=first_name,
137        last_name=last_name,
138        year_of_birth=year_of_birth,
139    )
140    my_expectation = (
141        f'Hello, my name is {first_name}'
142        f' {last_name} and I am'
143        f' {2026-year_of_birth}.'
144    )
145    assert reality == my_expectation
146
147
148# Exceptions seen
149# AssertionError
150# NameError
151# TypeError
152# AttributeError

  • I change reality for test_john to be the result of a call to the say_hello function of the person module in the src folder

     85def test_john():
 86    first_name = 'john'
 87    last_name = 'smith'
 88    sex = 'M'
 89    year_of_birth = 1580
 90
 91    reality = src.person.factory(
 92        first_name=first_name,
 93        last_name=last_name,
 94        sex=sex,
 95        year_of_birth=year_of_birth,
 96    )
 97    my_expectation = (
 98        f'{first_name}, {last_name},'
 99        f' {sex}, {year_of_birth}'
100    )
101    assert reality == my_expectation
102
103    # reality = say_hello(
104    reality = src.person.say_hello(
105        first_name=first_name,
106        last_name=last_name,
107        year_of_birth=year_of_birth,
108    )
109    my_expectation = (
110        # 'Hello, my name is jane'
111        f'Hello, my name is {first_name}'
112        f' {last_name} and I am'
113        f' {2026-year_of_birth}.'
114    )
115    assert reality == my_expectation
116
117
118def test_mary():

    the test is still green.

  • I remove the commented lines from test_john

     85def test_john():
 86    first_name = 'john'
 87    last_name = 'smith'
 88    sex = 'M'
 89    year_of_birth = 1580
 90
 91    reality = src.person.factory(
 92        first_name=first_name,
 93        last_name=last_name,
 94        sex=sex,
 95        year_of_birth=year_of_birth,
 96    )
 97    my_expectation = (
 98        f'{first_name}, {last_name},'
 99        f' {sex}, {year_of_birth}'
100    )
101    assert reality == my_expectation
102
103    reality = src.person.say_hello(
104        first_name=first_name,
105        last_name=last_name,
106        year_of_birth=year_of_birth,
107    )
108    my_expectation = (
109        f'Hello, my name is {first_name}'
110        f' {last_name} and I am'
111        f' {2026-year_of_birth}.'
112    )
113    assert reality == my_expectation
114
115
116def test_mary():

  • I change reality for test_joe to be the result of a call to the say_hello function of the person module in the src folder

    23def test_joe():
24    first_name = 'joe'
25    last_name = 'blow'
26    sex = 'M'
27    year_of_birth = 1996
28
29    reality = src.person.factory(
30        first_name=first_name,
31        last_name=last_name,
32        sex=sex,
33        year_of_birth=year_of_birth,
34    )
35    my_expectation = (
36        f'{first_name}, {last_name},'
37        f' {sex}, {year_of_birth}'
38    )
39    assert reality == my_expectation
40
41    # reality = say_hello(
42    reality = src.person.say_hello(
43        first_name=first_name,
44        last_name=last_name,
45        year_of_birth=year_of_birth,
46    )
47    my_expectation = (
48        f'Hello, my name is {first_name}'
49        f' {last_name} and I am'
50        f' {2026-year_of_birth}.'
51    )
52    assert reality == my_expectation
53
54
55def test_jane():

    the test is still green.

  • I remove the commented line from test_joe

    23def test_joe():
24    first_name = 'joe'
25    last_name = 'blow'
26    sex = 'M'
27    year_of_birth = 1996
28
29    reality = src.person.factory(
30        first_name=first_name,
31        last_name=last_name,
32        sex=sex,
33        year_of_birth=year_of_birth,
34    )
35    my_expectation = (
36        f'{first_name}, {last_name},'
37        f' {sex}, {year_of_birth}'
38    )
39    assert reality == my_expectation
40
41    reality = src.person.say_hello(
42        first_name=first_name,
43        last_name=last_name,
44        year_of_birth=year_of_birth,
45    )
46    my_expectation = (
47        f'Hello, my name is {first_name}'
48        f' {last_name} and I am'
49        f' {2026-year_of_birth}.'
50    )
51    assert reality == my_expectation
52
53
54def test_jane():

  • I change reality for test_jane to be the result of a call to the say_hello function of the person module in the src folder

    54def test_jane():
55    first_name = 'jane'
56    last_name = 'doe'
57    sex = 'F'
58    year_of_birth = 1991
59
60    reality = src.person.factory(
61        first_name=first_name,
62        last_name=last_name,
63        sex=sex,
64        year_of_birth=year_of_birth,
65    )
66    my_expectation = (
67        f'{first_name}, {last_name},'
68        f' {sex}, {year_of_birth}'
69    )
70    assert reality == my_expectation
71
72    # reality = say_hello(
73    reality = src.person.say_hello(
74        first_name=first_name,
75        last_name=last_name,
76        year_of_birth=year_of_birth,
77    )
78    my_expectation = (
79        f'Hello, my name is {first_name}'
80        f' {last_name} and I am'
81        f' {2026-year_of_birth}.'
82    )
83    assert reality == my_expectation
84
85
86def test_john():

    the test is still green.

  • I remove the commented line from test_jane

    54def test_jane():
55    first_name = 'jane'
56    last_name = 'doe'
57    sex = 'F'
58    year_of_birth = 1991
59
60    reality = src.person.factory(
61        first_name=first_name,
62        last_name=last_name,
63        sex=sex,
64        year_of_birth=year_of_birth,
65    )
66    my_expectation = (
67        f'{first_name}, {last_name},'
68        f' {sex}, {year_of_birth}'
69    )
70    assert reality == my_expectation
71
72    reality = src.person.say_hello(
73        first_name=first_name,
74        last_name=last_name,
75        year_of_birth=year_of_birth,
76    )
77    my_expectation = (
78        f'Hello, my name is {first_name}'
79        f' {last_name} and I am'
80        f' {2026-year_of_birth}.'
81    )
82    assert reality == my_expectation
83
84
85def test_john():

  • I remove the say_hello function from test_person.py

    1import src.person
2
3
4def test_joe():

    all the tests are still green because the calls that were made to the say_hello function that was in test_person.py are now made to the say_hello function in person.py in the src folder. When src.person.say_hello is called, Python follows this path

    src.person.say_hello
src
└── person.py
    └── def say_hello(
            first_name, last_name,
            year_of_birth
        ):
        ├── age = 2026 - year_of_birth
        │
        └── return (
                f'Hello, my name is {first_name}'
                f' {last_name} and I am {age}.'
            )

  • I add a git commit message in the other terminal

    git commit -am 'add say_hello function'

    the terminal shows a summary of the changes then goes back to the command line.

test_person

Since the solutions are separate from the tests, I can write the programs that make the tests pass without looking at test_person.py.

RED: make it fail

  • I close test_person.py

  • I delete all the text in person.py and the terminal shows 4 failures. I start with the last AttributeError

    FAILED ...::test_joe - AttributeError:
    module 'src.person' has no attribute 'factory'
FAILED ...::test_jane - AttributeError:
    module 'src.person' has no attribute 'factory'
FAILED ...::test_john - AttributeError:
    module 'src.person' has no attribute 'factory'
FAILED ...::test_mary - AttributeError:
    module 'src.person' has no attribute 'factory'
=================== 4 failed in A.BCs ===================

    Can you make the tests pass without looking at how I solve it below? You can come back to compare solutions when you are done or if you get stuck.

GREEN: make it pass

  • I add the name to person.py

    1factory

    the terminal is my friend, and shows NameError

    NameError: name 'factory' is not defined

  • I point factory to None (the simplest object) to define it

    1# factory
2factory = None

    the terminal is my friend, and shows TypeError

    TypeError: 'NoneType' object is not callable

    because factory points to None and I cannot call None like a function.

  • I change factory to a function to make it callable

    1# factory
2# factory = None
3def factory():
4    return None

    the terminal is my friend, and shows TypeError

    TypeError: factory() got
           an unexpected keyword argument
           'first_name'

    because this function definition does not allow any inputs, the parentheses are empty.

  • I add first_name in the parentheses so the function can take input

    1# factory
2# factory = None
3# def factory():
4def factory(first_name):
5    return None

    the terminal is my friend, and shows TypeError

    TypeError: factory() got
           an unexpected keyword argument 'last_name'.
           Did you mean 'first_name'?

    because the function definition now only allows one input (first_name) and it was called with a keyword argument (last_name).

  • I add last_name to the parentheses

    1# factory
2# factory = None
3# def factory():
4# def factory(first_name):
5def factory(first_name, last_name):
6    return None

    the terminal is my friend, and shows TypeError

    TypeError: factory() got
           an unexpected keyword argument 'sex'

    because the function definition only allows two inputs (first_name and last_name) and it was called with a keyword argument (sex).

  • I add sex to the parentheses

    1# factory
2# factory = None
3# def factory():
4# def factory(first_name):
5# def factory(first_name, last_name):
6def factory(first_name, last_name, sex):
7    return None

    the terminal is my friend, and shows TypeError

    TypeError: factory() got
           an unexpected keyword argument
           'year_of_birth'

    because the function definition only allows three inputs (first_name, last_name, sex) and it was called with a keyword argument (year_of_birth).

  • I add year_of_birth to the parentheses

     1# factory
 2# factory = None
 3# def factory():
 4# def factory(first_name):
 5# def factory(first_name, last_name):
 6# def factory(first_name, last_name, sex):
 7def factory(
 8        first_name, last_name,
 9        sex, year_of_birth,
10    ):
11    return None

    the terminal is my friend, and shows AssertionError

    AssertionError: assert None == 'mary, public, F, 2000'

  • I change the return statement to match the expectation of the test

     1# factory
 2# factory = None
 3# def factory():
 4# def factory(first_name):
 5# def factory(first_name, last_name):
 6# def factory(first_name, last_name, sex):
 7def factory(
 8        first_name, last_name,
 9        sex, year_of_birth,
10    ):
11    return 'mary, public, F, 2000'

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.person'
                has no attribute 'say_hello'

  • I add the name

     1say_hello
 2
 3
 4# factory
 5# factory = None
 6# def factory():
 7# def factory(first_name):
 8# def factory(first_name, last_name):
 9# def factory(first_name, last_name, sex):
10def factory(
11        first_name, last_name,
12        sex, year_of_birth,
13    ):
14    return 'mary, public, F, 2000'

    the terminal is my friend, and shows NameError

    NameError: name 'say_hello' is not defined

  • I point it to None to define it

    1# say_hello
2say_hello = None
3
4
5# factory

    the terminal is my friend, and shows TypeError

    TypeError: 'NoneType' object is not callable

    because say_hello points to None and I cannot call None like a function.

  • I make say_hello a function to make it callable

    1# say_hello
2# say_hello = None
3def say_hello():
4    return None
5
6
7# factory

    the terminal is my friend, and shows TypeError

    TypeError: say_hello() got
           an unexpected keyword argument
           'first_name'

    because this function definition does not allow any inputs, the parentheses are empty.

  • I add first_name in the parentheses

    1# say_hello
2# say_hello = None
3# def say_hello():
4def say_hello(first_name):
5    return None
6
7
8# factory

    the terminal is my friend, and shows TypeError

    TypeError: say_hello() got
           an unexpected keyword argument 'last_name'.
           Did you mean 'first_name'?

    because the function definition now only allows one input (first_name) and it was called with a keyword argument (last_name).

  • I add last_name to the parentheses

    1# say_hello
2# say_hello = None
3# def say_hello():
4# def say_hello(first_name):
5def say_hello(first_name, last_name):
6    return None
7
8
9# factory

    the terminal is my friend, and shows TypeError

    TypeError: say_hello() got
           an unexpected keyword argument
           'year_of_birth'

    because the function definition only allows two inputs (first_name and last_name) and it was called with a keyword argument (year_of_birth).

  • I add year_of_birth to the parentheses

     1# say_hello
 2# say_hello = None
 3# def say_hello():
 4# def say_hello(first_name):
 5# def say_hello(first_name, last_name):
 6def say_hello(
 7    first_name, last_name, year_of_birth,
 8):
 9    return None
10
11
12# factory

    the terminal is my friend, and shows AssertionError

    AssertionError: assert None
    == 'Hello, my name is mary public and I am 26.'

  • I use ctrl/command+c (Windows & Linux/MacOS) on the keyboard to copy the string from the terminal and ctrl/command+v to paste it to replace None in the return statement

     1# say_hello
 2# say_hello = None
 3# def say_hello():
 4# def say_hello(first_name):
 5# def say_hello(first_name, last_name):
 6def say_hello(
 7    first_name, last_name, year_of_birth,
 8):
 9    # return None
10    return 'Hello, my name is mary public and I am 26.'
11
12
13# factory

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'mary, public, F, 2000'
                    == 'john, smith, M, 1580'

    because the factory function always returns 'mary, public, F, 2000' and this test expects 'john, smith, M, 1580'.

  • I change the return statement of the factory function to see the difference between the input and the expected output (remember the identity function?)

    13# factory
14# factory = None
15# def factory():
16# def factory(first_name):
17# def factory(first_name, last_name):
18# def factory(first_name, last_name, sex):
19def factory(
20        first_name, last_name,
21        sex, year_of_birth,
22    ):
23    # return 'mary, public, F, 2000'
24    return first_name, last_name, sex, year_of_birth,

    the terminal is my friend, and shows AssertionError

    AssertionError: assert ('mary', 'public', 'F', 2000)
                     == 'mary, public, F, 2000'

    the first_name, last_name, sex and year_of_birth are part of the output.

  • I change the return statement to an f-string with those values

    13# factory
14# factory = None
15# def factory():
16# def factory(first_name):
17# def factory(first_name, last_name):
18# def factory(first_name, last_name, sex):
19def factory(
20        first_name, last_name,
21        sex, year_of_birth,
22    ):
23    # return 'mary, public, F, 2000'
24    # return first_name, last_name, sex, year_of_birth,
25    return (
26        f'{first_name}, {last_name},'
27        f' {sex}, {year_of_birth}'
28    )

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'Hello, my name ... and I am 26.'
                    == 'Hello, my name ...and I am 446.'

    because the say_hello function always returns 'Hello, my name is mary public and I am 26.' and this test expects 'Hello, my name is john smith and I am 446.'

  • I change the return statement of the say_hello function to see the difference between the input and the expected output

     1# say_hello
 2# say_hello = None
 3# def say_hello():
 4# def say_hello(first_name):
 5# def say_hello(first_name, last_name):
 6def say_hello(
 7    first_name, last_name, year_of_birth,
 8):
 9    # return None
10    # return 'Hello, my name is mary public and I am 26.'
11    return first_name, last_name, year_of_birth,
12
13
14# factory

    the terminal is my friend, and shows AssertionError

    AssertionError: assert ('mary', 'public', 'F', 2000)
                     == 'mary, public, F, 2000'

    the first_name and last_name are part of the output.

  • I change the return statement to an f-string with the input values

     1# say_hello
 2# say_hello = None
 3# def say_hello():
 4# def say_hello(first_name):
 5# def say_hello(first_name, last_name):
 6def say_hello(
 7    first_name, last_name, year_of_birth,
 8):
 9    # return None
10    # return 'Hello, my name is mary public and I am 26.'
11    # return first_name, last_name, year_of_birth,
12    return (
13        f'Hello, my name is {first_name}'
14        f' {last_name} and I am {year_of_birth}.'
15    )
16
17
18# factory

    the terminal is my friend, and shows AssertionError

    AssertionError: assert 'Hello, my name ...nd I am 2000.'
                    == 'Hello, my name ... and I am 26.'

    It looks like 26 is the age.

  • I change the year_of_birth value to a calculation of the age

     1# say_hello
 2# say_hello = None
 3# def say_hello():
 4# def say_hello(first_name):
 5# def say_hello(first_name, last_name):
 6def say_hello(
 7    first_name, last_name, year_of_birth,
 8):
 9    # return None
10    # return 'Hello, my name is mary public and I am 26.'
11    # return first_name, last_name, year_of_birth,
12    return (
13        f'Hello, my name is {first_name}'
14        # f' {last_name} and I am {year_of_birth}.'
15        f' {last_name} and I am'
16        f' {2026-year_of_birth}.'
17    )
18
19
20# factory

    all tests are green!

  • I remove the commented lines

     1def say_hello(
 2    first_name, last_name, year_of_birth,
 3):
 4    return (
 5        f'Hello, my name is {first_name}'
 6        f' {last_name} and I am'
 7        f' {2026-year_of_birth}.'
 8    )
 9
10
11def factory(
12        first_name, last_name,
13        sex, year_of_birth,
14    ):
15    return (
16        f'{first_name}, {last_name},'
17        f' {sex}, {year_of_birth}'
18    )

  • I add a git commit message in the new terminal

    git commit -am 'test person with f-strings'

close the project

  • I close person.py

  • I click in the terminal where the tests are running

  • I use q on the keyboard to leave the tests. The terminal goes back to the command line.

  • I change directory to the parent of person

    cd ..

    the terminal shows

    ...\pumping_python

    I am back in the pumping_python directory.

review

  • I ran tests to write one function that makes a person when given first_name, last_name, sex and year_of_birth so I do not have to make one function for each person.

  • I also ran tests to make another function that uses f-strings to make a string that represents the person I make saying hi when I give it first_name, last_name, and year_of_birth.

  • I saw the following Exceptions

  • My tests and solutions have a few problems,

    • Each test is basically the same two tests, there has to be a way that I can use one test for all the people.

    • The factory and say_hello functions use three of the same inputs

      • first_name

      • last_name

      • year_of_birth

      There has to be a better way<how to make a person with a class>, where I can give those values once, and get a representation for a person when I call the factory function and a message when I call the say_hello function.

For now, I am going to clean up the functions project so the tests and solutions are in separate files.

code from the chapter

Do you want to see all the CODE I typed in this chapter?

what is next?

Would you like to see me separate the tests and functions in the functions project?

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