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Check for python builtins being used as variables or parameters.

Project description

Flake8 Builtins plugin

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()

    max = list2[0]
    for x in list2:
        if x > 0:
            max = x

    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 "", line 17, in <module>
    max_values([3,4,5], [4,5,6])
  File "", 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): A002 argument "object" is shadowing a python builtin A002 argument "list" is shadowing a python builtin A002 argument "dict" is shadowing a python builtin A001 variable "max" is shadowing a python builtin A001 variable "min" is shadowing a python builtin 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 3.7, 3.8, 3.9, 3.10, 3.11, and pypy3

  • flake8


GPL 2.0


2.1.0 (2022-12-23)

  • Honor –builtins option from flake8 #73. [gforcada]

2.0.1 (2022-11-01)

  • Add official support for python 3.10 and 3.11. [gforcada] [michael-k]

  • Update options handling. [gforcada]

  • Simplify testing. [gforcada]

2.0.0 (2022-10-08)

  • Mark support for python 3.9. [lovetoburnswhen]

  • Replace travis for GitHub. [cclauss]

  • Fix CI badge. [sobolevn]

  • Make black and isort mandatory. [cclauss]

  • Drop python 2.7 and 3.6. [gforcada]

  • Overhaul GitHub actions to test on actual supported python versions. [gforcada]

  • New flake8 option –builtins-ignorelist to specify a list of builtins to ignore. [gsingh93]

1.5.3 (2020-05-14)

  • Change messages to have shorter text

1.5.2 (2020-03-16)

  • Add DictComp, SetComp, and GeneratorExpr support. [sobolevn]

1.5.1 (2020-03-16)

  • Adds kwonly and posonly args support. [sobolevn]

1.5.0 (2020-03-14)

  • Add python3.8 support. [sobolevn]

  • Add AnnAssign support. [soboelvn]

  • Add NamedExpr or := support. [sobolevn]

1.4.2 (2019-12-18)

  • Fix tuple parsing. [memery-imb]

1.4.1 (2018-05-11)

  • Fix regression in 1.4.0 and interaction with flake8-bugbear. [dirk-thomas]

1.4.0 (2018-05-03)

  • Make code more robust by not assuming that a node is an ast.Name but actually checking it. [gforcada]

  • Handle ast.Starred as well (i.e. a, *int = range(4)) [gforcada]

  • Handle lists as well, i.e. [a, int] = 3, 4 [gforcada]

1.3.1 (2018-04-30)

1.3.0 (2018-04-13)

1.2.3 (2018-04-10)

1.2.2 (2018-04-03)

1.2.1 (2018-04-01)

  • re-relase 1.2 from master branch. [gforcada]

1.2 (2018-04-01)

  • Fix error message in for loops. [gforcada]

  • Inspect the following places for possible builtins being shadowed:

    • with open(‘/tmp/bla.txt’) as int

    • except ValueError as int

    • [int for int in range(4)]

    • from zope.component import provide as int

    • import zope.component as int

    • class int(object)

    • def int()

    • async def int()

    • async for int in range(4)

    • async with open(‘/tmp/bla.txt’) as int


1.1.1 (2018-03-20)

  • Variables assigned in a for loop can be not only a Tuple, but a Tuple inside a Tuple. [dopplershift]

1.1.0 (2018-03-17)

  • Update more trove classifiers. [gforcada]

  • Inspect variables assigned in a for loop as well. Thanks to sobolevn for reporting it! [gforcada]

1.0.post0 (2017-12-02)

  • Update README. [DmytroLitvinov]

  • Update trove classifiers. [dirn]

1.0 (2017-08-19)

  • Use requirements.txt to pin dependencies. [gforcada]

  • Fix tests with newer flake8 version. [gforcada]

  • BREAKING CHANGE: error codes have been changed from B00X to A00X to not clash with flake8-bugbear, see [gforcada]

0.4 (2017-05-29)

  • Use a different code for class attributes. [karamanolev]

0.3.1.post0 (2017-05-27)

  • Release universal wheels, not only python 2 wheels. [gforcada]

  • Update trove classifiers. [gforcada]

0.3.1 (2017-05-27)

  • Fix stdin handling. [sangiovanni]

0.3 (2017-05-15)

  • Handle stdin, which is the way flake8 gets integrated into editors. [gforcada]

  • Test against Python 2.7, 3.5, 3.6 and pypy. [gforcada]

0.2 (2016-03-30)

  • Whitelist some builtins. [gforcada]

0.1 (2016-03-04)

  • Initial release [gforcada]

  • Add buildout and other stuff. [gforcada]

  • Add actual code. [gforcada]

  • Drop support for python 3.3, only python 2.7 and python 3.4 are tested. [gforcada]

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