what causes AttributeError?

So far, all the tests show that I get AttributeError when I use a name that is NOT in an object.

what is an attribute?

An attribute is a name (variable?) for something that belongs to an object (a class), for example, a human being has attributes like height, weight, sex and color, they are also known as properties.

preview

I have these tests by the end of the chapter

 1import src.attribute_error
 2import unittest
 3
 4
 5class TestAttributeError(unittest.TestCase):
 6
 7    def test_attribute_error_w_variables(self):
 8        src.attribute_error.variable_00
 9        src.attribute_error.variable_01
10        src.attribute_error.variable_02
11        src.attribute_error.variable_03
12        src.attribute_error.variable_04
13        src.attribute_error.variable_05
14        src.attribute_error.variable_06
15        src.attribute_error.variable_07
16        src.attribute_error.variable_08
17        src.attribute_error.variable_09
18
19    def test_attribute_error_w_functions(self):
20        src.attribute_error.function_00()
21        src.attribute_error.function_01()
22        src.attribute_error.function_02()
23        src.attribute_error.function_03()
24        src.attribute_error.function_04()
25        src.attribute_error.function_05()
26        src.attribute_error.function_06()
27        src.attribute_error.function_07()
28        src.attribute_error.function_08()
29        src.attribute_error.function_09()
30
31    def test_attribute_error_w_class_attributes(self):
32        src.attribute_error.AClass.attribute_00
33        src.attribute_error.AClass.attribute_01
34        src.attribute_error.AClass.attribute_02
35        src.attribute_error.AClass.attribute_03
36        src.attribute_error.AClass.attribute_04
37        src.attribute_error.AClass().attribute_05
38        src.attribute_error.AClass().attribute_06
39        src.attribute_error.AClass().attribute_07
40        src.attribute_error.AClass().attribute_08
41        src.attribute_error.AClass().attribute_09
42
43    def test_attribute_error_w_class_methods(self):
44        src.attribute_error.AClass.method_00()
45        src.attribute_error.AClass.method_01
46        src.attribute_error.AClass().method_02()
47        src.attribute_error.AClass().method_03
48        src.attribute_error.AClass().method_04()
49        src.attribute_error.AClass.method_05
50        src.attribute_error.AClass.method_06()
51        src.attribute_error.AClass.method_07
52        src.attribute_error.AClass().method_08()
53        src.attribute_error.AClass().method_09
54
55
56# Exceptions seen
57# AssertionError
58# AttributeError
59# NameError
60# TypeError
61# SyntaxError

start the project

  • I name this project attribute_error

  • I open a terminal

  • I use uv to make a directory for the project and initialize it

    uv init attribute_error

    the terminal shows

    Initialized project `attribute-error`
at `.../pumping_python/attribute_error`

    then goes back to the command line.

  • I change directory to the project

    cd attribute_error

    the terminal shows I am in the attribute_error folder

    .../pumping_python/attribute_error

  • I make a directory for the source code

    mkdir src

    the terminal goes back to the command line.

  • I use the mv program to change the name of main.py to attribute_error.py and move it to the src folder

    mv main.py src/attribute_error.py

    Move-Item main.py src/attribute_error.py

    the terminal goes back to the command line.

  • I make a directory for the tests

    mkdir tests

    the terminal goes back to the command line.

  • I make the tests directory a Python package

    Danger

    use 2 underscores (__) before and after init for __init__.py not _init_.py

    touch tests/__init__.py

    New-Item tests/__init__.py

    the terminal goes back to the command line.

  • I make a Python file for the tests in the tests directory

    touch tests/test_attribute_error.py

    New-Item tests/test_attribute_error.py

    the terminal goes back to the command line.

  • I open test_attribute_error.py

  • I add the first failing test to test_attribute_error.py

    1import unittest
2
3
4class TestAttributeError(unittest.TestCase):
5
6    def test_failure(self):
7        self.assertFalse(True)

  • I go back to the terminal to make a requirements file for the Python packages I need

    echo "pytest-watcher" > requirements.txt

    the terminal goes back to the command line.

  • I add the new files and folder to git for tracking

    git add .

    the terminal goes back to the command line.

  • I add a git commit message

    git commit -am 'setup project'

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

  • I use uv to install pytest-watcher with the requirements file

    uv add --requirement requirements.txt

    the terminal shows that it installed pytest-watcher and its dependencies.

  • I use pytest-watcher to run the tests automatically

    uv run pytest-watcher . --now

    the terminal is my friend, and shows AssertionError

    ======================== FAILURES ========================
________________ TestAttributeError.test_failure _________________

self = <tests.test_attribute_error.AttributeError testMethod=test_failure>

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

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

    because True is NOT False

    if the terminal does not show the same error, then check

    • if your tests/__init__.py has two underscores (__) before and after init for __init__.py not _init_.py

    • if you ran echo "pytest-watcher" > requirements.txt, to add pytest-watcher to the requirements file

    fix those errors and try to run uv run pytest-watcher . --now again

  • I add AssertionError to the list of Exceptions seen in test_attribute_error.py

     4class TestAttributeError(unittest.TestCase):
 5
 6    def test_failure(self):
 7        self.assertFalse(True)
 8
 9
10# Exceptions seen
11# AssertionError

  • then I change True to False in the assertion

    7        self.assertFalse(False)

    the test passes.

test_attribute_error_w_variables

RED: make it fail

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

    1import src.attribute_error
2import unittest

  • I change test_failure to test_attribute_error_w_variables

     5class TestAttributeError(unittest.TestCase):
 6
 7    def test_attribute_error_w_variables(self):
 8        src.attribute_error.variable_00
 9
10
11# Exceptions seen

    I think of src.attribute_error.variable_00 as an address

    • src is the src folder

    • src.attribute_error points to attribute_error.py in the src folder

    • src.attribute_error.variable_00 points to variable_00 in attribute_error.py in the src folder

    • since there is nothing in attribute_error.py named variable_00, Python cannot find variable_00 inside attribute_error.py and raises AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'variable_00'

    variable_00 is NOT an attribute of attribute_error.py in the src folder

  • I add AttributeError to the list of Exceptions seen in test_attribute_error.py

    11# Exceptions seen
12# AssertionError
13# AttributeError

GREEN: make it pass

  • I open attribute_error.py from the src folder of my Integrated Development Environment (IDE)

  • I delete all the text in the file, then add the name to attribute_error.py

    1variable_00

    the terminal is my friend, and shows NameError

    NameError: name 'variable_00' is not defined

    because I used a name that is not defined in this file

  • I add NameError to the list of Exceptions seen in test_attribute_error.py

    11# Exceptions seen
12# AssertionError
13# AttributeError
14# NameError

  • I point variable_00 to None, in attribute_error.py

    1variable_00 = None

    • the test passes because variable_00 is now an attribute/property of attribute_error.py in the src folder

    • I can use it from outside the file with src.attribute_error.variable_00

REFACTOR: make it better

  • I do the same test a few more times as a drill in test_attribute_error.py

     7    def test_attribute_error_w_variables(self):
 8        src.attribute_error.variable_00
 9        src.attribute_error.variable_01
10
11
12# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'variable_01'.
                Did you mean: 'variable_00'?

  • I add the name to attribute_error.py

    1variable_00 = None
2variable_01

    the terminal is my friend, and shows NameError

    NameError: name 'variable_01' is not defined

  • I point it to None to define it

    1variable_00 = None
2variable_01 = None

    the test passes.

  • I add another statement to test_attribute_error.py

     7    def test_attribute_error_w_variables(self):
 8        src.attribute_error.variable_00
 9        src.attribute_error.variable_01
10        src.attribute_error.variable_02
11
12
13# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'variable_02'.
                Did you mean: 'variable_00'?

  • I add the name and point it to None in attribute_error.py

    1variable_00 = None
2variable_01 = None
3variable_02 = None

    the test passes.

  • I add a line for src.attribute_error.variable_03 in test_attribute_error.py

     7    def test_attribute_error_w_variables(self):
 8        src.attribute_error.variable_00
 9        src.attribute_error.variable_01
10        src.attribute_error.variable_02
11        src.attribute_error.variable_03
12
13
14# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'variable_03'.
                Did you mean: 'variable_00'?

  • I add the variable to attribute_error.py

    1variable_00 = None
2variable_01 = None
3variable_02 = None
4variable_03 = None

    the test passes.

  • I add a line for src.attribute_error.variable_04 in test_attribute_error.py

     7    def test_attribute_error_w_variables(self):
 8        src.attribute_error.variable_00
 9        src.attribute_error.variable_01
10        src.attribute_error.variable_02
11        src.attribute_error.variable_03
12        src.attribute_error.variable_04
13
14
15# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'variable_04'.
                Did you mean: 'variable_00'?

  • I add the variable to attribute_error.py

    1variable_00 = None
2variable_01 = None
3variable_02 = None
4variable_03 = None
5variable_04 = None

    the test passes.

  • I add a line for src.attribute_error.variable_05 in test_attribute_error.py

     7    def test_attribute_error_w_variables(self):
 8        src.attribute_error.variable_00
 9        src.attribute_error.variable_01
10        src.attribute_error.variable_02
11        src.attribute_error.variable_03
12        src.attribute_error.variable_04
13        src.attribute_error.variable_05
14
15
16# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'variable_05'.
                Did you mean: 'variable_00'?

  • I add the variable to attribute_error.py

    1variable_00 = None
2variable_01 = None
3variable_02 = None
4variable_03 = None
5variable_04 = None
6variable_05 = None

    the test passes.

  • I add a line for src.attribute_error.variable_06 to test_attribute_error.py

     7    def test_attribute_error_w_variables(self):
 8        src.attribute_error.variable_00
 9        src.attribute_error.variable_01
10        src.attribute_error.variable_02
11        src.attribute_error.variable_03
12        src.attribute_error.variable_04
13        src.attribute_error.variable_05
14        src.attribute_error.variable_06
15
16
17# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'variable_06'.
                Did you mean: 'variable_00'?

  • I add the variable to attribute_error.py

    1variable_00 = None
2variable_01 = None
3variable_02 = None
4variable_03 = None
5variable_04 = None
6variable_05 = None
7variable_06 = None

    the test passes.

  • I add a line for src.attribute_error.variable_07 to test_attribute_error.py

     7    def test_attribute_error_w_variables(self):
 8        src.attribute_error.variable_00
 9        src.attribute_error.variable_01
10        src.attribute_error.variable_02
11        src.attribute_error.variable_03
12        src.attribute_error.variable_04
13        src.attribute_error.variable_05
14        src.attribute_error.variable_06
15        src.attribute_error.variable_07
16
17
18# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'variable_07'.
                Did you mean: 'variable_00'?

  • I add the variable to attribute_error.py

    1variable_00 = None
2variable_01 = None
3variable_02 = None
4variable_03 = None
5variable_04 = None
6variable_05 = None
7variable_06 = None
8variable_07 = None

    the test passes.

  • I add a line for src.attribute_error.variable_08 to test_attribute_error.py

     7    def test_attribute_error_w_variables(self):
 8        src.attribute_error.variable_00
 9        src.attribute_error.variable_01
10        src.attribute_error.variable_02
11        src.attribute_error.variable_03
12        src.attribute_error.variable_04
13        src.attribute_error.variable_05
14        src.attribute_error.variable_06
15        src.attribute_error.variable_07
16        src.attribute_error.variable_08
17
18
19# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'variable_08'.
                Did you mean: 'variable_00'?

  • I add the variable to attribute_error.py

    1variable_00 = None
2variable_01 = None
3variable_02 = None
4variable_03 = None
5variable_04 = None
6variable_05 = None
7variable_06 = None
8variable_07 = None
9variable_08 = None

    the test passes.

  • I add a line for src.attribute_error.variable_09 to test_attribute_error.py

     7    def test_attribute_error_w_variables(self):
 8        src.attribute_error.variable_00
 9        src.attribute_error.variable_01
10        src.attribute_error.variable_02
11        src.attribute_error.variable_03
12        src.attribute_error.variable_04
13        src.attribute_error.variable_05
14        src.attribute_error.variable_06
15        src.attribute_error.variable_07
16        src.attribute_error.variable_08
17        src.attribute_error.variable_09
18
19
20# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'variable_09'.
                Did you mean: 'variable_00'?

  • I add the variable to attribute_error.py

     1variable_00 = None
 2variable_01 = None
 3variable_02 = None
 4variable_03 = None
 5variable_04 = None
 6variable_05 = None
 7variable_06 = None
 8variable_07 = None
 9variable_08 = None
10variable_09 = None

    the test passes.

  • I open a new terminal then change directories to assertion_error

    cd assertion_error

    the terminal shows I am in the assertion_error folder

    .../pumping_python/assertion_error

  • I add a git commit message

    git commit -am \
'add test_what_is_an_assertion'

A variable in a module is an attribute of the module.

test_attribute_error_w_functions

RED: make it fail

I add a test for functions to test_attribute_error.py

15        src.attribute_error.variable_07
16        src.attribute_error.variable_08
17        src.attribute_error.variable_09
18
19    def test_attribute_error_w_functions(self):
20        src.attribute_error.function_00()
21
22
23# Exceptions seen

the terminal is my friend, and shows AttributeError

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

GREEN: make it pass

  • I add the name and point it to None in attribute_error.py

     1variable_00 = None
 2variable_01 = None
 3variable_02 = None
 4variable_03 = None
 5variable_04 = None
 6variable_05 = None
 7variable_06 = None
 8variable_07 = None
 9variable_08 = None
10variable_09 = None
11
12
13function_00 = None

    the terminal is my friend, and shows TypeError

    TypeError: 'NoneType' object is not callable

    because I cannot call None like a function.

  • I add TypeError to the list of Exceptions seen in test_attribute_error.py

    23# Exceptions seen
24# AssertionError
25# AttributeError
26# NameError
27# TypeError

  • I change the variable to a function in attribute_error.py

    13# function_00 = None
14def function_00():
15    return None

    • the test passes because function_00 is now an attribute/property of attribute_error.py in the src folder

    • I can call it from outside the file with src.attribute_error.function_00()

REFACTOR: make it better

  • I remove the commented line

     1variable_00 = None
 2variable_01 = None
 3variable_02 = None
 4variable_03 = None
 5variable_04 = None
 6variable_05 = None
 7variable_06 = None
 8variable_07 = None
 9variable_08 = None
10variable_09 = None
11
12
13def function_00():
14    return None

    time to make it a drill.

  • I add a call to src.attribute_error.function_01 in test_attribute_error_w_functions in test_attribute_error.py

    19    def test_attribute_error_w_functions(self):
20        src.attribute_error.function_00()
21        src.attribute_error.function_01()
22
23
24# Exceptions seen

    the terminal is my friend, and shows AttributeError

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

  • I add the function to attribute_error.py

    13def function_00():
14    return None
15
16
17def function_01():
18    return None

    the test passes.

  • I add a line for src.attribute_error.function_02 to test_attribute_error_w_functions in test_attribute_error.py

    13    def test_attribute_error_w_functions(self):
14        src.attribute_error.function_00()
15        src.attribute_error.function_01()
16        src.attribute_error.function_02()
17
18
19# Exceptions seen

    the terminal is my friend, and shows AttributeError

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

  • I add a function for it in attribute_error.py

    17def function_01():
18    return None
19
20
21def function_02():
22    return None

    the test passes.

  • I add a line for src.attribute_error.function_03 to test_attribute_error_w_functions in test_attribute_error.py

    19    def test_attribute_error_w_functions(self):
20        src.attribute_error.function_00()
21        src.attribute_error.function_01()
22        src.attribute_error.function_02()
23        src.attribute_error.function_03()
24
25
26# Exceptions seen

    the terminal is my friend, and shows AttributeError

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

  • I add a function for it in attribute_error.py

    21def function_02():
22    return None
23
24
25def function_03():
26    return None

    the test passes.

  • I add a line for src.attribute_error.function_04 to test_attribute_error_w_functions in test_attribute_error.py

    19    def test_attribute_error_w_functions(self):
20        src.attribute_error.function_00()
21        src.attribute_error.function_01()
22        src.attribute_error.function_02()
23        src.attribute_error.function_03()
24        src.attribute_error.function_04()
25
26
27# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'function_04'.
                Did you mean: 'function_00'?

  • I add a function for it in attribute_error.py

    25def function_03():
26    return None
27
28
29def function_04():
30    return None

    the test passes.

  • I add a line for src.attribute_error.function_05 to test_attribute_error_w_functions in test_attribute_error.py

    19    def test_attribute_error_w_functions(self):
20        src.attribute_error.function_00()
21        src.attribute_error.function_01()
22        src.attribute_error.function_02()
23        src.attribute_error.function_03()
24        src.attribute_error.function_04()
25        src.attribute_error.function_05()
26
27
28# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'function_05'.
                Did you mean: 'function_00'?

  • I add a function for it in attribute_error.py

    29def function_04():
30    return None
31
32
33def function_05():
34    return None

    the test passes.

  • I add a line for src.attribute_error.function_06 to test_attribute_error_w_functions in test_attribute_error.py

    19    def test_attribute_error_w_functions(self):
20        src.attribute_error.function_00()
21        src.attribute_error.function_01()
22        src.attribute_error.function_02()
23        src.attribute_error.function_03()
24        src.attribute_error.function_04()
25        src.attribute_error.function_05()
26        src.attribute_error.function_06()
27
28
29# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'function_06'.
                Did you mean: 'function_00'?

  • I add a function for it in attribute_error.py

    33def function_05():
34    return None
35
36
37def function_06():
38    return None

    the test passes.

  • I add a line for src.attribute_error.function_07 to test_attribute_error_w_functions in test_attribute_error.py

    19    def test_attribute_error_w_functions(self):
20        src.attribute_error.function_00()
21        src.attribute_error.function_01()
22        src.attribute_error.function_02()
23        src.attribute_error.function_03()
24        src.attribute_error.function_04()
25        src.attribute_error.function_05()
26        src.attribute_error.function_06()
27        src.attribute_error.function_07()
28
29
30# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'function_07'.
                Did you mean: 'function_00'?

  • I add a function for it in attribute_error.py

    37def function_06():
38    return None
39
40
41def function_07():
42    return None

    the test passes.

  • I add a line for src.attribute_error.function_08 to test_attribute_error_w_functions in test_attribute_error.py

    19    def test_attribute_error_w_functions(self):
20        src.attribute_error.function_00()
21        src.attribute_error.function_01()
22        src.attribute_error.function_02()
23        src.attribute_error.function_03()
24        src.attribute_error.function_04()
25        src.attribute_error.function_05()
26        src.attribute_error.function_06()
27        src.attribute_error.function_07()
28        src.attribute_error.function_08()
29
30
31# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'function_08'.
                Did you mean: 'function_00'?

  • I add a function for it in attribute_error.py

    41def function_07():
42    return None
43
44
45def function_08():
46    return None

    the test passes.

  • I add a line for src.attribute_error.function_09 to test_attribute_error_w_functions in test_attribute_error.py

    19    def test_attribute_error_w_functions(self):
20        src.attribute_error.function_00()
21        src.attribute_error.function_01()
22        src.attribute_error.function_02()
23        src.attribute_error.function_03()
24        src.attribute_error.function_04()
25        src.attribute_error.function_05()
26        src.attribute_error.function_06()
27        src.attribute_error.function_07()
28        src.attribute_error.function_08()
29        src.attribute_error.function_09()
30
31
32# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: module 'src.attribute_error'
                has no attribute 'function_09'.
                Did you mean: 'function_00'?

  • I add a function for it in attribute_error.py

    45def function_08():
46    return None
47
48
49def function_09():
50    return None

    the test passes.

  • I add a git commit message in the other terminal

    git commit -am \
'add test_attribute_error_w_functions'

  • A function in a module is an attribute of the module

  • A variable in a module is an attribute of the module

test_attribute_error_w_class_attributes

The tests show that variables and functions in a module are attributes of the module.

Is a class in a module also an attribute of the module?

RED: make it fail

  • I go back to the terminal that is running the tests

I add a test for class attributes to test_attribute_error.py

26        src.attribute_error.function_06()
27        src.attribute_error.function_07()
28        src.attribute_error.function_08()
29        src.attribute_error.function_09()
30
31    def test_attribute_error_w_class_attributes(self):
32        src.attribute_error.AClass.attribute_00
33
34
35# Exceptions seen

the terminal is my friend, and shows AttributeError

AttributeError: module 'src.attribute_error'
                has no attribute 'AClass'

GREEN: make it pass

  • I add a function to attribute_error.py

    49def function_09():
50    return None
51
52
53def AClass():
54    return None

    the terminal is my friend, and shows AttributeError

    AttributeError: 'function' object
                has no attribute 'attribute_00'

  • I add a variable to the function

    53def AClass():
54
55    attribute_00 = None
56    return None

    the terminal still shows the same Exception because I cannot get to a variable inside a function from outside the function. The variable is only used within the function when it runs.

  • I use the class keyword to change AClass from a function to a class

    53# def AClass():
54class AClass(object):
55
56    attribute_00 = None
57    return None

    the terminal is my friend, and shows SyntaxError

    E    return None
E    ^^^^^^^^^^^
E  SyntaxError: 'return' outside function

    because I cannot use a return statement outside a function.

  • I add SyntaxError to the list of Exceptions seen in test_attribute_error.py

    35# Exceptions seen
36# AssertionError
37# AttributeError
38# NameError
39# TypeError
40# SyntaxError

  • I comment out the return statement from AClass in attribute_error.py since it is no longer a function

    53# def AClass():
54class AClass(object):
55
56    attribute_00 = None
57    # return None

    • the test passes because attribute_00 is now an attribute/property of the AClass class

    • AClass is an attribute of the attribute_error.py module in the src folder

    • I can use attribute_00 from outside the file with src.attribute_error.AClass.attribute_00 or src.attribute_error.AClass().attribute_00

REFACTOR: make it better

  • I remove the commented lines

    49def function_09():
50    return None
51
52
53class AClass(object):
54
55    attribute_00 = None

  • I add a line for src.attribute_error.AClass.attribute_01 to test_attribute_error.py

    31    def test_attribute_error_w_class_attributes(self):
32        src.attribute_error.AClass.attribute_00
33        src.attribute_error.AClass.attribute_01
34
35
36# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'attribute_01'.
                Did you mean: 'attribute_00'?

  • I add the name to the class definition in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None

    the test passes.

  • I add a line for src.attribute_error.AClass.attribute_02 to test_attribute_error.py

    31    def test_attribute_error_w_class_attributes(self):
32        src.attribute_error.AClass.attribute_00
33        src.attribute_error.AClass.attribute_01
34        src.attribute_error.AClass.attribute_02
35
36
37# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'attribute_02'.
                Did you mean: 'attribute_00'?

  • I add the name to the class definition in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None

    the test passes.

  • I add a line for src.attribute_error.AClass.attribute_03 to test_attribute_error.py

    31    def test_attribute_error_w_class_attributes(self):
32        src.attribute_error.AClass.attribute_00
33        src.attribute_error.AClass.attribute_01
34        src.attribute_error.AClass.attribute_02
35        src.attribute_error.AClass.attribute_03
36
37
38# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'attribute_03'.
                Did you mean: 'attribute_00'?

  • I add the name to the class definition in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None

    the test passes.

  • I add a line for src.attribute_error.AClass.attribute_04 to test_attribute_error.py

    31    def test_attribute_error_w_class_attributes(self):
32        src.attribute_error.AClass.attribute_00
33        src.attribute_error.AClass.attribute_01
34        src.attribute_error.AClass.attribute_02
35        src.attribute_error.AClass.attribute_03
36        src.attribute_error.AClass.attribute_04
37
38
39# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'attribute_04'.
                Did you mean: 'attribute_00'?

  • I add the name to the class definition in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None
59    attribute_04 = None

    the test passes.

  • I add a line for src.attribute_error.AClass().attribute_05 to test_attribute_error.py

    31    def test_attribute_error_w_class_attributes(self):
32        src.attribute_error.AClass.attribute_00
33        src.attribute_error.AClass.attribute_01
34        src.attribute_error.AClass.attribute_02
35        src.attribute_error.AClass.attribute_03
36        src.attribute_error.AClass.attribute_04
37        src.attribute_error.AClass().attribute_05
38
39
40# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'attribute_05'.
                Did you mean: 'attribute_00'?

  • I add the name to the class definition in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None
59    attribute_04 = None
60    attribute_05 = None

    the test passes because in this case it does not matter if I use the class (AClass) or an instance of the class (AClass()).

  • I add a line for src.attribute_error.AClass().attribute_06 to test_attribute_error.py

    31    def test_attribute_error_w_class_attributes(self):
32        src.attribute_error.AClass.attribute_00
33        src.attribute_error.AClass.attribute_01
34        src.attribute_error.AClass.attribute_02
35        src.attribute_error.AClass.attribute_03
36        src.attribute_error.AClass.attribute_04
37        src.attribute_error.AClass().attribute_05
38        src.attribute_error.AClass().attribute_06
39
40
41# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'attribute_06'.
                Did you mean: 'attribute_00'?

  • I add the name to the class definition in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None
59    attribute_04 = None
60    attribute_05 = None
61    attribute_06 = None

    the test passes.

  • I add a line for src.attribute_error.AClass().attribute_07 to test_attribute_error.py

    31    def test_attribute_error_w_class_attributes(self):
32        src.attribute_error.AClass.attribute_00
33        src.attribute_error.AClass.attribute_01
34        src.attribute_error.AClass.attribute_02
35        src.attribute_error.AClass.attribute_03
36        src.attribute_error.AClass.attribute_04
37        src.attribute_error.AClass().attribute_05
38        src.attribute_error.AClass().attribute_06
39        src.attribute_error.AClass().attribute_07
40
41
42# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'attribute_07'.
                Did you mean: 'attribute_00'?

  • I add the name to the class definition in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None
59    attribute_04 = None
60    attribute_05 = None
61    attribute_06 = None
62    attribute_07 = None

    the test passes.

  • I add a line for src.attribute_error.AClass().attribute_08 to test_attribute_error.py

    31    def test_attribute_error_w_class_attributes(self):
32        src.attribute_error.AClass.attribute_00
33        src.attribute_error.AClass.attribute_01
34        src.attribute_error.AClass.attribute_02
35        src.attribute_error.AClass.attribute_03
36        src.attribute_error.AClass.attribute_04
37        src.attribute_error.AClass().attribute_05
38        src.attribute_error.AClass().attribute_06
39        src.attribute_error.AClass().attribute_07
40        src.attribute_error.AClass().attribute_08
41
42
43# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'attribute_08'.
                Did you mean: 'attribute_00'?

  • I add the name to the class definition in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None
59    attribute_04 = None
60    attribute_05 = None
61    attribute_06 = None
62    attribute_07 = None
63    attribute_08 = None

    the test passes.

  • I add a line for src.attribute_error.AClass().attribute_09 to test_attribute_error.py

    31    def test_attribute_error_w_class_attributes(self):
32        src.attribute_error.AClass.attribute_00
33        src.attribute_error.AClass.attribute_01
34        src.attribute_error.AClass.attribute_02
35        src.attribute_error.AClass.attribute_03
36        src.attribute_error.AClass.attribute_04
37        src.attribute_error.AClass().attribute_05
38        src.attribute_error.AClass().attribute_06
39        src.attribute_error.AClass().attribute_07
40        src.attribute_error.AClass().attribute_08
41        src.attribute_error.AClass().attribute_09
42
43
44# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'attribute_09'.
                Did you mean: 'attribute_00'?

  • I add the name to the class definition in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None
59    attribute_04 = None
60    attribute_05 = None
61    attribute_06 = None
62    attribute_07 = None
63    attribute_08 = None
64    attribute_09 = None

    the test passes.

  • I add a git commit message in the other terminal

    git commit -am \
'add test_attribute_error_w_class_attributes'

  • A variable in a class is an attribute of the class

  • A class in a module is an attribute of the module

  • A function in a module is an attribute of the module

  • A variable in a module is an attribute of the module

test_attribute_error_w_class_methods

The tests show that variables, functions and classes in a module are attributes of the module, and variables in a class are attributes of the class.

Methods of a class are also attributes of the class.

RED: make it fail

  • I go back to the terminal that is running the tests

  • I add a test for methods to test_attribute_error.py

    38        src.attribute_error.AClass().attribute_06
39        src.attribute_error.AClass().attribute_07
40        src.attribute_error.AClass().attribute_08
41        src.attribute_error.AClass().attribute_09
42
43    def test_attribute_error_w_class_methods(self):
44        src.attribute_error.AClass.method_00()
45
46
47# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'method_00'

GREEN: make it pass

  • I add the name to AClass and point it to None, in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None
59    attribute_04 = None
60    attribute_05 = None
61    attribute_06 = None
62    attribute_07 = None
63    attribute_08 = None
64    attribute_09 = None
65
66    method_00 = None

    the terminal is my friend, and shows TypeError

    TypeError: 'NoneType' object is not callable

    because method_00 points to None and I cannot call None like a function.

  • I use the def keyword to change it from a variable (attribute) to a method

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None
59    attribute_04 = None
60    attribute_05 = None
61    attribute_06 = None
62    attribute_07 = None
63    attribute_08 = None
64    attribute_09 = None
65
66    # method_00 = None
67    def method_00():
68        return None

    • the test passes because method_00 is now an attribute/property of the AClass class

    • AClass is an attribute of the attribute_error.py module in the src folder

    • I can call method_00 from outside the file with src.attribute_error.AClass.method_00() or src.attribute_error.AClass().method_00()

REFACTOR: make it better

  • I remove the commented line

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None
59    attribute_04 = None
60    attribute_05 = None
61    attribute_06 = None
62    attribute_07 = None
63    attribute_08 = None
64    attribute_09 = None
65
66    def method_00():
67        return None

  • You know the “drill”, I add a line for src.attribute_error.AClass.method_01 to test_attribute_error.py

    43    def test_attribute_error_w_class_methods(self):
44        src.attribute_error.AClass.method_00()
45        src.attribute_error.AClass.method_01
46
47
48# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'method_01'.
                Did you mean: 'method_00'?

  • I add the method to the definition of AClass in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None
59    attribute_04 = None
60    attribute_05 = None
61    attribute_06 = None
62    attribute_07 = None
63    attribute_08 = None
64    attribute_09 = None
65
66    def method_00():
67        return None
68
69    def method_01():
70        return None

    the test passes because in this case it does not matter if I reference the method (AClass.method_01) or call it (AClass.method_01()).

  • I add a line for src.attribute_error.AClass.method_02 to test_attribute_error.py

    43    def test_attribute_error_w_class_methods(self):
44        src.attribute_error.AClass.method_00()
45        src.attribute_error.AClass.method_01
46        src.attribute_error.AClass().method_02()
47
48
49# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'method_02'.
                Did you mean: 'method_00'?

  • I add the method to the definition of AClass in attribute_error.py

    69    def method_01():
70        return None
71
72    def method_02():
73        return None

    the terminal is my friend, and shows TypeError

    TypeError: AClass.method_02() takes
           0 positional arguments but 1 was given

    because this happens when AClass().method_02() is called

    AClass().method_02()
    AClass.method_02(AClass)

    which raises TypeError since the definition of method_02 does not allow it take any positional arguments (the parentheses are empty).

  • I add self to the parentheses of method_02

    72    # def method_02():
73    def method_02(self):
74        return None

    the test passes because this happens when AClass().method_02() is called

    AClass().method_02()
    AClass.method_02(self)

    where self is AClass.

  • I add the staticmethod decorator method definition instead of self since it does not use anything in the class. That way I do not send more information than what the method needs.

    69    def method_01():
70        return None
71
72    @staticmethod
73    def method_02():
74    # def method_02(self):
75        return None

    the test is still green because this now happens when AClass().method_02() is called

    AClass().method_02()
    AClass.method_02()

    with the staticmethod decorator it does not matter if I call the method from an instance (AClass()) or from the class (AClass).

  • I remove the commented line

    69    def method_01():
70        return None
71
72    @staticmethod
73    def method_02():
74        return None

  • I add a line for src.attribute_error.AClass.method_03 to test_attribute_error.py

    43    def test_attribute_error_w_class_methods(self):
44        src.attribute_error.AClass.method_00()
45        src.attribute_error.AClass.method_01
46        src.attribute_error.AClass().method_02()
47        src.attribute_error.AClass().method_03
48
49
50# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'method_03'.
                Did you mean: 'method_00'?

  • I add the method to the definition of AClass in attribute_error.py

    72    @staticmethod
73    def method_02():
74        return None
75
76    def method_03():
77        return None

    the test passes because in this case I reference the method (AClass().method_03), I do not call it (AClass().method_03()).

  • I add a line for src.attribute_error.AClass.method_04 to test_attribute_error.py

    43    def test_attribute_error_w_class_methods(self):
44        src.attribute_error.AClass.method_00()
45        src.attribute_error.AClass.method_01
46        src.attribute_error.AClass().method_02()
47        src.attribute_error.AClass().method_03
48        src.attribute_error.AClass().method_04()
49
50
51# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'method_04'.
                Did you mean: 'method_00'?

  • I add the method to the definition of AClass in attribute_error.py

    76    def method_03():
77        return None
78
79    def method_04():
80        return None

    the terminal is my friend, and shows TypeError

    TypeError: AClass.method_04() takes
           0 positional arguments but 1 was given

    because this happens when AClass().method_04() is called

    AClass().method_04()
    AClass.method_04(AClass)

    which raises TypeError since the definition of method_04 does not allow it take any positional arguments.

  • I add the staticmethod decorator to the definition for method_04

    76    def method_03():
77        return None
78
79    @staticmethod
80    def method_04():
81        return None

    the test passes because this now happens when AClass().method_04() is called

    AClass().method_04()
    AClass.method_04()

    with the staticmethod decorator it does not matter if I call the method from an instance (AClass()) or from the class (AClass).

  • I add a line for src.attribute_error.AClass.method_05 to test_attribute_error.py

    43    def test_attribute_error_w_class_methods(self):
44        src.attribute_error.AClass.method_00()
45        src.attribute_error.AClass.method_01
46        src.attribute_error.AClass().method_02()
47        src.attribute_error.AClass().method_03
48        src.attribute_error.AClass().method_04()
49        src.attribute_error.AClass.method_05
50
51
52# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'method_05'.
                Did you mean: 'method_00'?

  • I add the method to the definition of AClass in attribute_error.py

    79    @staticmethod
80    def method_04():
81        return None
82
83    def method_05():
84        return None

    the test passes.

  • I add a line for src.attribute_error.AClass.method_06 to test_attribute_error.py

    43    def test_attribute_error_w_class_methods(self):
44        src.attribute_error.AClass.method_00()
45        src.attribute_error.AClass.method_01
46        src.attribute_error.AClass().method_02()
47        src.attribute_error.AClass().method_03
48        src.attribute_error.AClass().method_04()
49        src.attribute_error.AClass.method_05
50        src.attribute_error.AClass.method_06()
51
52
53# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'method_06'.
                Did you mean: 'method_00'?

  • I add the method to the definition of AClass in attribute_error.py

    83    def method_05():
84        return None
85
86    def method_06():
87        return None

    the test passes because this happens when AClass.method_06() is called

    AClass.method_06()

    I called the method with the class (AClass.method_06()) not an instance of the class (AClass().method_06()).

  • I add a line for src.attribute_error.AClass.method_07 to test_attribute_error.py

    43    def test_attribute_error_w_class_methods(self):
44        src.attribute_error.AClass.method_00()
45        src.attribute_error.AClass.method_01
46        src.attribute_error.AClass().method_02()
47        src.attribute_error.AClass().method_03
48        src.attribute_error.AClass().method_04()
49        src.attribute_error.AClass.method_05
50        src.attribute_error.AClass.method_06()
51        src.attribute_error.AClass.method_07
52
53
54# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'method_07'.
                Did you mean: 'method_00'?

  • I add the method to the definition of AClass in attribute_error.py

    86    def method_06():
87        return None
88
89    def method_07():
90        return None

    the test passes.

  • I add a line for src.attribute_error.AClass.method_08 to test_attribute_error.py

    43    def test_attribute_error_w_class_methods(self):
44        src.attribute_error.AClass.method_00()
45        src.attribute_error.AClass.method_01
46        src.attribute_error.AClass().method_02()
47        src.attribute_error.AClass().method_03
48        src.attribute_error.AClass().method_04()
49        src.attribute_error.AClass.method_05
50        src.attribute_error.AClass.method_06()
51        src.attribute_error.AClass.method_07
52        src.attribute_error.AClass().method_08()
53
54
55# Exceptions seen

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'method_08'.
                Did you mean: 'method_00'?

  • I add the method to the definition of AClass in attribute_error.py

    89    def method_07():
90        return None
91
92    def method_08():
93        return None

    the terminal is my friend, and shows TypeError

    TypeError: AClass.method_08() takes
           0 positional arguments but 1 was given

    because this happens when AClass().method_08() is called

    AClass().method_08()
    AClass.method_08(AClass)

    which raises TypeError since the definition of method_08 does not allow it take any positional arguments (the parentheses are empty).

  • I add the staticmethod decorator to the method definition since it does not use anything in the class

    89    def method_07():
90        return None
91
92    @staticmethod
93    def method_08():
94        return None

    the test passes because this now happens when AClass().method_08() is called

    AClass().method_08()
    AClass.method_08()

    with the staticmethod decorator it does not matter if I call the method from an instance (AClass()) or from the class (AClass).

  • I add a line for src.attribute_error.AClass.method_09 to test_attribute_error.py

    43    def test_attribute_error_w_class_methods(self):
44        src.attribute_error.AClass.method_00()
45        src.attribute_error.AClass.method_01
46        src.attribute_error.AClass().method_02()
47        src.attribute_error.AClass().method_03
48        src.attribute_error.AClass().method_04()
49        src.attribute_error.AClass.method_05
50        src.attribute_error.AClass.method_06()
51        src.attribute_error.AClass.method_07
52        src.attribute_error.AClass().method_08()
53        src.attribute_error.AClass().method_09
54
55
56# Exceptions seen
57# AssertionError
58# AttributeError
59# NameError
60# TypeError
61# SyntaxError

    the terminal is my friend, and shows AttributeError

    AttributeError: type object 'AClass'
                has no attribute 'method_09'.
                Did you mean: 'method_00'?

  • I add the method to the definition of AClass in attribute_error.py

    53class AClass(object):
54
55    attribute_00 = None
56    attribute_01 = None
57    attribute_02 = None
58    attribute_03 = None
59    attribute_04 = None
60    attribute_05 = None
61    attribute_06 = None
62    attribute_07 = None
63    attribute_08 = None
64    attribute_09 = None
65
66    def method_00():
67        return None
68
69    def method_01():
70        return None
71
72    @staticmethod
73    def method_02():
74        return None
75
76    def method_03():
77        return None
78
79    @staticmethod
80    def method_04():
81        return None
82
83    def method_05():
84        return None
85
86    def method_06():
87        return None
88
89    def method_07():
90        return None
91
92    @staticmethod
93    def method_08():
94        return None
95
96    def method_09():
97        return None

    the test passes because in this case I reference the method (AClass().method_09), I do not call it (AClass().method_09()).

  • I add a git commit message in the other terminal

    git commit -am \
'add test_attribute_error_w_class_methods'

  • A function in a class is an attribute of the class and is called a method

  • A variable in a class is an attribute of the class

  • A class in a module is an attribute of the module

  • A function in a module is an attribute of the module

  • A variable in a module is an attribute of the module

because in Python everything is an object.

close the project

  • I close attribute_error.py and test_attribute_error.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 attribute_error

    cd ..

    the terminal shows

    .../pumping_python

    I am back in the pumping_python directory

review

I ran tests for AttributeError with

I also saw these Exceptions

code from the chapter

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

what is next?

I know

Would you like to test None (the simplest object)?

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