flake8-indent-in-def

This is a flake8 plugin enforces 8-space indentation in function/class definitions in Python code.

Installation

pip install flake8-indent-in-def

Violation codes

There is one violation code that this plugin reports:

Code	Description
IND101	hanging indentation in function definition must be 8 spaces
IND102	if the 1st argument is on the same line as the function name, all other arguments must be on the same line
IND201	hanging indentation in class definition must be 8 spaces
IND202	if the 1st base class is on the same line as the class name, all other base classes must be on the same line

Style examples

Wrong

This plugin considers the following indentation styles wrong:

def some_function(arg1,
                  *,
                  arg2,
                  arg3):
    print(arg1)

def some_function(argument1,
                  argument2,
                  argument3, argument4, argumen5):
    print(argument1)

This following style above is the style choice of the black formatter. Both this plugin and PEP8 consider it wrong because arguments and function names would be difficult to visually distinghish.

def some_function(
    arg1: int,
    arg2: list,
    arg3: bool = None,
):
    print(arg1)

Correct

Correspondingly, here are the correct indentation styles:

def some_function(
        arg1: int,
        arg2: list,
        *,
        arg3: bool = None,
):
    print(arg1)

def some_function(
        arg1: int, arg2: list, arg3: bool = None
) -> None:
    print(arg1)

def some_function(arg1: int, arg2: list, arg3: bool = None) -> None:
    print(arg1)

def some_function(
        arg1: int, arg2: list,
        arg3: bool = None, arg4: float = 2.0,
) -> None:
    print(arg1)

Additionally, this plugin by default enforces the same indentation styles on class inheritence:

class MyClass(
        BaseClassA,
        BaseClassB,
        BaseClassC,
):
    def __init__(self):
        pass

You can opt out of class inheritence checks by ignoring rules IND201 and IND202.

Notes

• This plugin does not check trailing commas, because flake8-commas already does it
• This plugin does not forbid grouping arguments (see example below), because WPS317 can enforce it

def some_func(
        arg1, arg2, arg3,
        arg4, arg5,
):
    pass

Rationale

When we only indent by 4 spaces in function definitions, it is difficult to visually distinguish function arguments with the function name and the function body. This reduces readability. It is similar for base classes in class definitions, but it's less of an issue than function definitions.

Specifically, the following style is allowed by PEP8 but this plugin still consider it wrong, because it could lead to messy code diff when refactoring:

- def some_very_very_very_long_func(arg1,
+ def some_very_very_very_very_very_long_func(arg1,
                                    arg2,
                                    arg3,

):
    return None

Interaction with other style checkers and formatters

• By design, black-formatted code will cause a style violation here, because black authors explicitly opted for the 4-space indentation and do not plan to change it
• The style enforced in this plugin contradicts with rule WPS318 enforced by wemake-python-styleguide ("WPS")
  • But WPS is configurable, so you can always opt out of WPS318
• You can use py-def-indent-formatter right after black to make your code satisfy the style requirements of this plugin