Check for python builtins being used as variables or parameters

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()
    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.

Example

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

Install with pip:

$ pip install flake8-builtins

Requirements

• Python 2.7, 3.6, 3.7, 3.8
• flake8

License

GPL 2.0