TypeError

preview

I have these tests by the end of the chapter

 1import src.type_error
 2import unittest
 3
 4
 5class TestTypeError(unittest.TestCase):
 6
 7    def test_type_error_w_the_uncallables(self):
 8        src.type_error.none()
 9        src.type_error.false()
10        src.type_error.true()
11        src.type_error.an_integer()
12        src.type_error.a_float()
13        src.type_error.a_string()
14        src.type_error.a_tuple()
15        src.type_error.a_list()
16        src.type_error.a_set()
17        src.type_error.a_dictionary()
18
19    def test_type_error_w_function_signatures(self):
20        src.type_error.function_00('a')
21        src.type_error.function_01('a', 'b')
22        src.type_error.function_02('a', 'b', 'c')
23        src.type_error.function_03('a', 'b', 'c', 'd')
24
25    def test_type_error_w_objects_that_do_not_mix(self):
26        with self.assertRaises(TypeError):
27            None + False
28        with self.assertRaises(TypeError):
29            True - 'text'
30        with self.assertRaises(TypeError):
31            (0, 1, 2, 'n') * [0, 1, 2, 'n']
32        with self.assertRaises(TypeError):
33            {0, 1, 2, 'n'} / {'key': 'value'}
34
35
36# Exceptions seen
37# AssertionError
38# AttributeError
39# TypeError

questions about TypeError

Questions to think about as I go through the chapter

start the project

  • I open a terminal

  • I type pwd to make sure I am in the pumping_python folder

    pwd

    the terminal goes back to the command line.

    .../pumping_python

    Note

    if you are not in the pumping_python folder, try cd ~/pumping_python

  • I name this project type_error

  • I open makePythonTdd.sh or makePythonTdd.ps1 in the editor

    Tip

    Here is a quick way to open makePythonTdd.sh or makePythonTdd.ps1 if you are using Visual Studio Code

    code makePythonTdd.sh

    on Windows without Windows Subsystem for Linux use

    code makePythonTdd.ps1

  • I change everywhere I have exceptions to the name of this project

     1#!/bin/bash
 2mkdir type_error
 3cd type_error
 4mkdir src
 5touch src/type_error.py
 6mkdir tests
 7touch tests/__init__.py
 8
 9echo "import unittest
10
11
12class TestTypeError(unittest.TestCase):
13
14    def test_failure(self):
15        self.assertFalse(True)
16
17
18# Exceptions seen
19# AssertionError
20" > tests/test_type_error.py

    Note

    on Windows without Windows Subsystem for Linux use makePythonTdd.ps1 NOT makePythonTdd.sh

     1mkdir type_error
 2cd type_error
 3mkdir src
 4New-Item src/type_error.py
 5mkdir tests
 6New-Item tests/__init__.py
 7
 8"import unittest
 9
10
11class TestTypeError(unittest.TestCase):
12
13    def test_failure(self):
14        self.assertFalse(True)
15
16# Exceptions seen
17# AssertionError
18" | Out-File tests/test_type_error.py

  • I run the program in the terminal

    ./makePythonTdd.sh

    Note

    on Windows without Windows Subsystem for Linux use makePythonTdd.ps1 NOT makePythonTdd.sh

    ./makePythonTdd.ps1

    the terminal is my friend, and shows AssertionError

    ================================= FAILURES =================================
_________________________ TestTypeError.test_failure _________________________

self = <tests.test_exceptions.TestTypeError testMethod=test_failure>

    def test_failure(self):
>       self.assertFalse(True)
E       AssertionError: True is not false

tests/test_type_error.py:7: AssertionError
====================== short test summary info ========================
FAILED tests/test_type_error.py::TestTypeError::test_failure - AssertionError: True is not false
============================ 1 failed in X.YZs =============================

  • I hold ctrl (Windows/Linux) or option/command (MacOS) on the keyboard and use the mouse to click on tests/test_type_error.py:7 to put the cursor on line 7 in the editor

  • then I change True to False

    7        self.assertFalse(False)

    the test passes.

test_type_error_w_the_uncallables

There are objects that can NOT be called

RED: make it fail

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

    1import src.type_error
2import unittest

  • I change test_failure to test_type_error_w_the_uncallables with a failing line

    5class TestTypeError(unittest.TestCase):
6
7    def test_type_error_w_the_uncallables(self):
8        src.type_error.none()

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'none'

    there is nothing in type_error.py in the src folder yet

  • I add AttributeError to the list of Exceptions seen

    11# Exceptions seen
12# AssertionError
13# AttributeError

GREEN: make it pass

I can call a function, I cannot call None

REFACTOR: make it better

  • I add another failing line to test_type_error.py

    7    def test_type_error_w_the_uncallables(self):
8        src.type_error.none()
9        src.type_error.false()

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'false'

    nothing is named false in type_error.py

  • I add the name to type_error.py and point it to False

    1def none():
2    return None
3
4
5false = False

    the terminal is my friend, and shows TypeError

    TypeError: 'bool' object is not callable

    I cannot call a boolean like a function

  • I change the variable to a function

    1def none():
2    return None
3
4def false():
5    return False

    the test is green again

  • I add a line to test the other boolean in test_type_error.py

     7    def test_type_error_w_the_uncallables(self):
 8        src.type_error.none()
 9        src.type_error.false()
10        src.type_error.true()

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'true'

    there is nothing named true in type_error.py

  • I add the name and point it to True in type_error.py

    5def false():
6    return False
7
8
9true = True

    the terminal is my friend, and shows TypeError

    TypeError: 'bool' object is not callable

  • I make it a function

     5def false():
 6    return False
 7
 8
 9def true():
10    return True

    the test passes. I can call a function, I cannot call a boolean or None

  • I add a line that will fail to test_type_error.py

     8        src.type_error.none()
 9        src.type_error.false()
10        src.type_error.true()
11        src.type_error.an_integer()

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'an_integer'

  • I add the name and point it to an integer in type_error.py

     9def true():
10    return True
11
12
13an_integer = 1234

    the terminal is my friend, and shows TypeError

  • I change the variable to a function

     9def true():
10    return True
11
12
13def an_integer():
14    return 1234

    the test passes. I can call a function, I cannot call an integer, a boolean or None

  • I add a line for a float in test_type_error.py

     9        src.type_error.false()
10        src.type_error.true()
11        src.type_error.an_integer()
12        src.type_error.a_float()

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'a_float'

  • I add the name and point it to a float in type_error.py

    13def an_integer():
14    return 1234
15
16
17a_float = 1.234

    the terminal is my friend, and shows TypeError

    TypeError: 'float' object is not callable

  • I make a_float a function to make it callable

    13def an_integer():
14    return 1234
15
16
17def a_float():
18    return 1.234

    the test passes. I can call a function, I cannot call a float, integer, boolean or None

  • I add a line for a string (anything in quotes) in test_type_error.py

    10        src.type_error.true()
11        src.type_error.an_integer()
12        src.type_error.a_float()
13        src.type_error.a_string()

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'a_string'

  • I add the name and point it to a string in type_error.py

    17def a_float():
18    return 1.234
19
20
21a_string = 'a string'

    the terminal is my friend, and shows TypeError

    TypeError: 'str' object is not callable

  • I change a_string to a function

    17def a_float():
18    return 1.234
19
20
21def a_string():
22    return 'a string'

    the test passes. I can call a function. I cannot call a string, float, integer, boolean or None

  • I add a failing line for a tuple (anything in parentheses (), separated by a comma) in test_type_error.py

    11        src.type_error.an_integer()
12        src.type_error.a_float()
13        src.type_error.a_string()
14        src.type_error.a_tuple()

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'a_tuple'

  • I add the name and point it to a tuple in type_error.py

    21def a_string():
22    return 'a string'
23
24
25a_tuple = (1, 2, 3, 'n')

    the terminal is my friend, and shows TypeError

    TypeError: 'tuple' object is not callable

  • I change it to a function

    21def a_string():
22    return 'a string'
23
24
25def a_tuple():
26    return (1, 2, 3, 'n')

    the test passes. I can call a function. I cannot call a tuple, string, float, integer, boolean or None

  • I add another line to test_type_error.py

    12        src.type_error.a_float()
13        src.type_error.a_string()
14        src.type_error.a_tuple()
15        src.type_error.a_list()

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'a_list'

  • I add the name and point it to a list (anything in square brackets ([]) in type_error.py

    25def a_tuple():
26    return (1, 2, 3, 'n')
27
28
29a_list = [1, 2, 3, 'n']

    the terminal is my friend, and shows TypeError

    TypeError: 'list' object is not callable

  • I change a_list to a function

    25def a_tuple():
26    return (1, 2, 3, 'n')
27
28
29def a_list():
30    return [1, 2, 3, 'n']

    the test passes. I can call a function, I cannot call a list, tuple, string, float, integer, boolean or None

  • I add another failing line to test_type_error.py

    13        src.type_error.a_string()
14        src.type_error.a_tuple()
15        src.type_error.a_list()
16        src.type_error.a_set()

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'a_set'

  • I add the name and point it to a set in type_error.py

    29def a_list():
30    return [1, 2, 3, 'n']
31
32
33a_set = {1, 2, 3, 'n'}

    the terminal is my friend, and shows TypeError

    TypeError: 'set' object is not callable

  • I make it a function

    29def a_list():
30    return [1, 2, 3, 'n']
31
32
33def a_set():
34    return {1, 2, 3, 'n'}

    the test passes. I can call a function, I cannot call a set, list, tuple, string, float, integer, boolean or None

  • I add the last failing line for this test to test_type_error.py

     7    def test_type_error_w_the_uncallables(self):
 8        src.type_error.none()
 9        src.type_error.false()
10        src.type_error.true()
11        src.type_error.an_integer()
12        src.type_error.a_float()
13        src.type_error.a_string()
14        src.type_error.a_tuple()
15        src.type_error.a_list()
16        src.type_error.a_set()
17        src.type_error.a_dictionary()
18
19
20# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'a_dictionary'

  • I add the name and point it to a dictionary in type_error.py

    33def a_set():
34    return {1, 2, 3, 'n'}
35
36
37a_dictionary = {'key': 'value'}

    the terminal is my friend, and shows TypeError

    TypeError: 'dict' object is not callable

  • I change it to a function

    33def a_set():
34    return {1, 2, 3, 'n'}
35
36
37def a_dictionary():
38    return {'key': 'value'}

    the test is green again. I can call a function, I cannot call a dictionary, set, list, tuple, string, float, integer, boolean or None

It is safe to say that I cannot call data structures because they are NOT callable. I can call functions, they are callable

test_type_error_w_function_signatures

When I call a function I have to match its definition also known as its signature or I get TypeError

RED: make it fail

  • I add a new test to test_type_error.py

    17        src.type_error.a_dictionary()
18
19    def test_type_error_w_function_signatures(self):
20        src.type_error.function_00('a')
21
22
23# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'function_00'

GREEN: make it pass

  • I add the function to type_error.py

    37def a_dictionary():
38    return {'key': 'value'}
39
40
41def function_00():
42    return None

    the terminal is my friend, and shows TypeError

    TypeError: function_00() takes 0 positional arguments
           but 1 was given

    because function_00 is called with 'a' as input and the definition does not allow any inputs

  • I add a name in parentheses to the function definition

    41def function_00(the_input):
42    return None

    the test passes.

I have to call a function in a way that matches its definition or I get TypeError

REFACTOR: make it better

  • I add a new failing line to test_type_error.py

    19def test_type_error_w_function_signatures(self):
20    src.type_error.function_00('a')
21    src.type_error.function_01('a', 'b')

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'function_01'. Did you mean: 'function_00'?

  • I add the function to type_error.py

    41def function_00(the_input):
42    return None
43
44
45def function_01(the_input):
46    return None

    the terminal is my friend, and shows TypeError

    TypeError: function_01() takes 1 positional argument but 2 were given

    the definition only allows one input, and the test sent two

  • I change the first name, then add another name in parentheses so that the call to the function and its definition match

    45def function_01(first, second):
46    return None

    the test passes.

  • I add another failing line to test_type_error.py

    19    def test_type_error_w_function_signatures(self):
20        src.type_error.function_00('a')
21        src.type_error.function_01('a', 'b')
22        src.type_error.function_02('a', 'b', 'c')

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'function_02'. Did you mean: 'function_00'?

  • I add the function to type_error.py

    45def function_01(first, second):
46    return None
47
48
49def function_02(first, second):
50    return None

    the terminal is my friend, and shows TypeError

    TypeError: function_02() takes 2 positional arguments but 3 were given

  • I add another name in parentheses to make the number of inputs match

    49def function_02(first, second, third):
50    return None

    the test passes.

  • I add one more failing line to test_type_error.py

    19    def test_type_error_w_function_signatures(self):
20        src.type_error.function_00('a')
21        src.type_error.function_01('a', 'b')
22        src.type_error.function_02('a', 'b', 'c')
23        src.type_error.function_03('a', 'b', 'c', 'd')

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.type_error' has no attribute 'function_03'. Did you mean: 'function_00'?

  • I add the function to type_error.py

    49def function_02(first, second, third):
50    return None
51
52
53def function_03(first, second, third):
54    return None

    the terminal is my friend, and shows TypeError

    TypeError: function_03() takes 3 positional arguments but 4 were given

  • I add a 4th name in parentheses to the definition

    53def function_03(first, second, third, fourth):
54    return None

    the test passes.

I have to call a function with the same number of inputs its definition expects

test_type_error_w_objects_that_do_not_mix

Some operations do not work if the objects are NOT the same type

RED: make it fail

I add a new test with a failing line in test_type_error.py

23        src.type_error.function_03('a', 'b', 'c', 'd')
24
25    def test_type_error_w_objects_that_do_not_mix(self):
26        None + False
27
28
29# Exceptions seen

the terminal is my friend, and shows TypeError

TypeError: unsupported operand type(s) for +: 'NoneType' and 'bool'

I cannot do arithmetic with None

GREEN: make it pass

I add the assertRaises method

25    def test_type_error_w_objects_that_do_not_mix(self):
26        with self.assertRaises(TypeError):
27            None + False

the test passes.

REFACTOR: make it better

  • I add another failing line to the test

    25    def test_type_error_w_objects_that_do_not_mix(self):
26        with self.assertRaises(TypeError):
27            None + False
28        True - 'text'

    the terminal is my friend, and shows TypeError

    TypeError: unsupported operand type(s) for -: 'bool' and 'str'

  • I use assertRaises to handle the Exception

    25    def test_type_error_w_objects_that_do_not_mix(self):
26        with self.assertRaises(TypeError):
27            None + False
28        with self.assertRaises(TypeError):
29            True - 'text'

    the test passes.

  • I add another failing line

    25    def test_type_error_w_objects_that_do_not_mix(self):
26        with self.assertRaises(TypeError):
27            None + False
28        with self.assertRaises(TypeError):
29            True - 'text'
30        (0, 1, 2, 'n') * [0, 1, 2, 'n']

    the terminal is my friend, and shows TypeError

    TypeError: can't multiply sequence by non-int of type 'list'

  • I add assertRaises

    25    def test_type_error_w_objects_that_do_not_mix(self):
26        with self.assertRaises(TypeError):
27            None + False
28        with self.assertRaises(TypeError):
29            True - 'text'
30        with self.assertRaises(TypeError):
31            (0, 1, 2, 'n') * [0, 1, 2, 'n']
32
33# Exceptions seen

    the test passes.

  • I add another failing line

    25    def test_type_error_w_objects_that_do_not_mix(self):
26        with self.assertRaises(TypeError):
27            None + False
28        with self.assertRaises(TypeError):
29            True - 'text'
30        with self.assertRaises(TypeError):
31            (0, 1, 2, 'n') * [0, 1, 2, 'n']
32        {0, 1, 2, 'n'} / {'key': 'value'}

    the terminal is my friend, and shows TypeError

    TypeError: unsupported operand type(s) for /: 'set' and 'dict'

  • I add assertRaises

    25def test_type_error_w_objects_that_do_not_mix(self):
26    with self.assertRaises(TypeError):
27        None + False
28    with self.assertRaises(TypeError):
29        True - 'text'
30    with self.assertRaises(TypeError):
31        (0, 1, 2, 'n') * [0, 1, 2, 'n']
32    with self.assertRaises(TypeError):
33        {0, 1, 2, 'n'} / {'key': 'value'}

    the terminal is my friend, and shows all tests are passing

close the project

  • I close test_type_error.py and type_error.py in the editor

  • then I click in the terminal and exit the tests with ctrl/command+c on the keyboard, the terminal goes back to the command line.

  • I change directory to the parent of type_error

    cd ..

    the terminal is my friend, and shows

    ...\pumping_python

    I am back in the pumping_python directory

review

I ran tests for TypeError with

How many questions can you answer after going through this chapter?

code from the chapter

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

what is next?

you know

Would you like to use what you know so far with the Calculator?

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