what is a module?

A Python module is a file that ends in .py. Any folder that contains an __init__.py is also a Python module

what causes ModuleNotFoundError?

ModuleNotFoundError is raised when Python cannot find a module given in an import statement

preview

These are the tests I have by the end of the chapter

import unittest


class TestModuleNotFoundError(unittest.TestCase):

    def test_module_not_found_error(self):
        import src.module_00
        import src.module_01
        import src.module_02
        import src.module_03
        import src.module_04
        import src.module_05
        import src.module_06
        import src.module_07
        import src.module_08
        import src.module_09


# Exceptions seen
# AssertionError
# ModuleNotFoundError

start the project

I open a terminal to run makePythonTdd.sh with module_not_found_error as the name of the project
```
./makePythonTdd.sh module_not_found_error
```
Note

on Windows without Windows Subsystem for Linux use makePythonTdd.ps1 instead of makePythonTdd.sh
```
./makePythonTdd.ps1 module_not_found_error
```
it makes the folders and files that are needed, installs packages, runs the first test, and the terminal shows AssertionError
```
E       AssertionError: True is not false

tests/test_module_not_found_error.py:7: AssertionError
```
I hold ctrl (Windows/Linux) or option/command (MacOS) on the keyboard and use the mouse to click on tests/test_module_not_found_error.py:7 to put the cursor on line 7 in the editor
then I change True to False in the assertion
```
7        self.assertFalse(False)
```
the test passes
I change the name of the class to match the CapWords format to follow Python convention
```
4class TestModuleNotFoundError(unittest.TestCase):
```

test_module_not_found_error

RED: make it fail

I change test_failure to test_module_not_found_error

import unittest

class TestModuleNotFoundError(unittest.TestCase):

    def test_module_not_found_error(self):
        import src.module_00

the terminal shows ModuleNotFoundError

ModuleNotFoundError: No module called 'src.module_00'

because Python cannot find module_00.py in the src folder

I add ModuleNotFoundError to the list of Exceptions seen in test_module_not_found_error.py
```
10# Exceptions seen
11# AssertionError
12# ModuleNotFoundError
```

GREEN: make it pass

I change module_not_found_error.py in the src folder to module_00.py and the test passes

REFACTOR: make it better

I add another import statement to test_module_not_found_error.py

    def test_module_not_found_error(self):
        import src.module_00
        import src.module_01

the terminal shows ModuleNotFoundError

ModuleNotFoundError: No module named 'src.module_01'

I make a new file named module_01.py in the src folder, the test passes and I close the file

I continue with another import statement in test_module_not_found_error.py

    def test_module_not_found_error(self):
        import src.module_00
        import src.module_01
        import src.module_02

the terminal shows ModuleNotFoundError

ModuleNotFoundError: No module called 'src.module_02'

I add module_02.py to the src folder and the test is green again again, I close the file

I add another import statement in test_module_not_found_error.py

    def test_module_not_found_error(self):
        import src.module_00
        import src.module_01
        import src.module_02
        import src.module_03

the terminal shows

ModuleNotFoundError: No module called 'src.module_03'

I add the file to the src folder and the test passes, I close the file

I add an import statement to test_module_not_found_error.py

        import src.module_03
        import src.module_04


# Exceptions seen

the terminal shows ModuleNotFoundError

ModuleNotFoundError: No module named 'src.module_04'

I add module_04.py to the src folder, the test passes and I close the file

I add another import statement to test_module_not_found_error.py

        import src.module_04
        import src.module_05


# Exceptions seen

the terminal shows ModuleNotFoundError

ModuleNotFoundError: No module named 'src.module_05'

I add the file to the src folder, the test passes and I close the file

another import statement in test_module_not_found_error.py

        import src.module_05
        import src.module_06


# Exceptions seen

the terminal shows ModuleNotFoundError

ModuleNotFoundError: No module named 'src.module_06'

I add module_06.py to the src folder, the test passes, and I close the file

I add an import statement in test_module_not_found_error.py

        import src.module_06
        import src.module_07


# Exceptions seen

the terminal shows ModuleNotFoundError

ModuleNotFoundError: No module named 'src.module_07'

I add the module to the src folder, the test passes and I close the file

I add an import statement to test_module_not_found_error.py

        import src.module_07
        import src.module_08


# Exceptions seen

the test passes

I add module_08.py to the src folder, the test passes

I add the last import statement to test_module_not_found_error.py

        import src.module_08
        import src.module_09


# Exceptions seen

the terminal shows ModuleNotFoundError

ModuleNotFoundError: No module named 'src.module_09'

I add the file to the src folder and the test passes

close the project

I close test_module_not_found_error.py in the editor
I click in the terminal, then use q on the keyboard to leave the tests. The terminal goes back to the command line
- I change directory to the parent of module_not_found_error
```
cd ..
```
  the terminal shows
```
...\pumping_python
```
  I am back in the pumping_python directory

review

I ran a test for ModuleNotFoundError to practice making Python modules

code from the chapter

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

what is next?

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