Better dev exp

Here we will learn about function annotations, docstrings, and formatting styles.

Function Annotation

• In Python 3 we can specify the type of our arguments and what our function returns.
• They’re optional metadata info.

[!NOTE]

Though the main idea was introduced in PEP 3107 and PEP 484 but from version 3.5 onward we have a typing section in the Python’s doc. So be sure to read those PEPs and docs thoroughly since type-safety of your code, and its maintainability depends on it IMO.

def place_order(
        product_id: int,
        quantity: int,
        /,
        discount_code: str=None,
        *,
        shipping_address: str,
        expedited: bool=False) -> None:
    pass

[!TIP]

You’ll learn about modules here, but just for now you just need to know that they are like a toolbox with prebuilt tools ready for you to use them. And in that toolbox we have a tool (module) called typing.

typing.Tuple and typing.List are Generic types; this means you can specify what type their contents must be e.g. a list of integers:

import typing
numbers: typing.List[int] = [1, 2]

But from version 3.5 we do not need to use these generic types exported from typing module. But instead we can use the built-in types, i.e.:

numbers: list[int] = [3, 4]

What is important is to keep in mind that this is the new preferred way of type annotating stuff.

Docstring

• First line:
  • Always short.
  • Concise summary of the function’s purpose.
  • Begin with a capital letter and end with a period.
• If it is multiline, second line should be blank.
• The 3rd line going forward you can write a description about your function. Things like:
  • Calling conventions.
  • Return value.
  • etc.

def place_order(
        product_id: int,
        quantity: int,
        /,
        discount_code: str=None,
        *,
        shipping_address: str,
        expedited: bool=False) -> None:
    """
    Places an order for a product.

    Arguments:
    - product_id (int): ID of the product (positional-only)
    - quantity (int): Quantity to order (positional-only)
    - discount_code (str): Optional promo code (positional-or-keyword)
    - shipping_address (str): Required keyword-only address
    - expedited (bool): Optional, keyword-only flag for fast shipping
    """
    pass

[!TIP]

You can learn how to write good docstring by going through PEP 0256, PEP 0257 and PEP 0258.

Formatting Styles

• Making your code more readable is always a good idea, and adopting a nice coding style can help that tremendously.
• PEP 8 is our style guide as I mentioned it from time to time.

Most Important Points Extracted from PEP 8

• Use docstrings.
• Use 4-space indentation, no tabs.
• Wrap lines so that they do NOT exceed 79 characters.
• Write comments in a separate line whenever possible.
• Use blank lines to separate functions, classes, and larger blocks of code inside functions.

• Spaces:

  • After commas.
  • Around operators.

  result = max(1, 2) + max(3, 4)
  

• Consistent function/class naming:

  • Class: PascalCase.
  • Methods/functions: snake_case.

  We talked about naming conventions here.

• self as the name for the first method argument (will discuss it when we learned classes in Python).
• Try to use plain English and not fancy characters or some chars that needs a different encoding than utf-8 (we talked about encoding here).

VSCode Extensions

Here we’ll go over some of the most useful extensions in VSCode for coding in Python.

autopep8

1. Open "Extensions", press `Ctrl+Shift+x` or click on its icon on the left hand side panel:  2. Search for "[autopep8](https://marketplace.visualstudio.com/items?itemName=ms-python.autopep8)" and click on install button.  3. Open "Settings" by pressing `Ctrl+comma` or clicking on the gear icon on the bottom left corner of VSCode:  4. Then search for "Format On Save" and check it:  5. Configure autopep8 to be your default code formatter. To do that we need to open command palette by pressing `Ctrl+Shift+p` and type "format document with":  6. Press enter and autopep8 should be your default formatter.  If not click on the "Configure Default Formatter":  7. And we need to configure it to not cross 79 line length define by PEP 8:  [You can learn how to do it step by step here](https://stackoverflow.com/a/74370180/8784518). > [!CAUTION] > > This extension in my experience does not do a very good job. So be sure to read the PEP 8 just in case it was messing with your code.

Pylint

Nice suggestions to improve your code quality.

Mypy Type Checker

An extension so that when you have a nicely annotated code like this your VSCode shows you a squiggly red line under it, indicating that something is wrong there: ```py var: list[int] = [1, '2', 3] ```

Flake8

An extension for showing errors in your code that are more of a syntactical issue. E.g. here it will draw a squiggly line under `bogus` since it is a valid type. ```py def a(aaaaaaaaaaaaaaa: int, bbbbbbbbbbbbbb: bogus): pass ```

Pylance

An extension for showing intellisense. E.g. when you type `"a string"` and press dot it should show a complete list of all methods available in Python.

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