Check for python builtins being used as variables or parameters.

Imagine some code like this:

def max_values(list, list2):
    max = list[0]
    for x in list:
        if x > 0:
            max = x
    all_values = list()
    all_values.append(max)
    max = list2[0]
    for x in list2:
        if x > 0:
            max = x
    all_values.append(max)
    return all_values
max_values([3, 4, 5, ], [5, 6, 7])

The last statement is not returning [5, 7] as one would expect, instead is raising this exception:

Traceback (most recent call last):
  File "test.py", line 17, in <module>
    max_values([3,4,5], [4,5,6])
  File "bla.py", line 6, in max_values
    all_values = list()
TypeError: 'list' object is not callable

Why? Because max_value function's first argument is list a Python builtin. Python allows to override them, but although could be useful in some really specific use cases, the general approach is to not do that as code then can suddenly break without a clear trace.

Given the following code:

def my_method(object, list, dict):
    max = 5
    min = 3
    zip = (4, 3)

The following warnings are shown (via flake8):

test.py:1:15: A002 argument "object" is shadowing a python builtin
test.py:1:23: A002 argument "list" is shadowing a python builtin
test.py:1:29: A002 argument "dict" is shadowing a python builtin
test.py:2:5: A001 variable "max" is shadowing a python builtin
test.py:3:5: A001 variable "min" is shadowing a python builtin
test.py:4:5: A001 variable "zip" is shadowing a python builtin

Install with pip:

$ python -m pip install flake8-builtins

One can use --builtins-ignorelist option, or configuration option, to ignore a custom list of builtins:

$ flake8 --builtins-ignorelist id,copyright *.py

• Python 3.8, 3.9, 3.10, 3.11, 3.12, and pypy3
• flake8

A001:

A variable is shadowing a Python builtin.

A002:

An argument is shadowing a Python builtin.

A003:

A class attribute is shadowing a Python builtin.

A004:

An import statement is shadowing a Python builtin.

A005:

A module is shadowing a Python builtin module (e.g: logging or socket)

A006:

A lambda argument is shadowing a Python builtin.

GPL 2.0