part-4.md

Session 3.4: Imports and structuring projects (15:45 - 16:30)

Show how imports work (15 min)

Write a script called hello.py with the following code:

def greet(name):
    message = 'hello {0}, how is it going?'.format(name)
    return message


# just to test it works
print(greet('bob'))

Write a script called main.py with the following code:

message = greet('alice')

print(message)

• Test hello.py.
• Try main.py. It fails, discuss why.
• Together fix main.py.
• Once you fix main.py you will see this output:

$ python main.py

hello bob, how is it going?
hello alice, how is it going?

• Discuss why we see this.
• Add the following code to hello.py and observe what happens when you run hello.py or main.py:

print(f'__name__ in hello.py evaluates to {__name__}')

• Solve this problem by introducing this structure:

if __name__ == '__main__':
    # ...
    # ...

Exercise: Structuring projects (30 min)

As an exercise we will improve an example script.

In groups of two:

• First test it out and browse it a bit and read the code.

Together:

• We answer questions about the code.
• We discuss the possible problems or bugs in this script.

In groups of two:

• Collect all code into functions. Discuss why.
• Collect reusable functions into modules. Discuss why.
• If you introduce external dependencies, collect the dependencies into requirements.txt. Discuss why.
• Check your code with pycodestyle.

Together we discuss:

• Possible solutions.
• Underscore convention.
• requirements.txt or Pipfile.