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type-comparison (E721)

Added in v0.0.39 · Related issues · View source

Derived from the pycodestyle linter.

What it does

Checks for object type comparisons using == and other comparison operators.

Why is this bad?

Unlike a direct type comparison, isinstance will also check if an object is an instance of a class or a subclass thereof.

If you want to check for an exact type match, use is or is not.

Known problems

When using libraries that override the == (__eq__) operator (such as NumPy, Pandas, and SQLAlchemy), this rule may produce false positives, as converting from == to is or is not will change the behavior of the code.

For example, the following operations are not equivalent:

import numpy as np

np.array([True, False]) == False
# array([False,  True])

np.array([True, False]) is False
# False

Example

if type(obj) == type(1):
    pass

if type(obj) == int:
    pass

Use instead:

if isinstance(obj, int):
    pass