Rule Definition
In Python, a variable under assignment in a given scope will be by default considered as local to that scope (and thus dynamically created when absent). Any variable in the outer scope with the same name will be shadowed. This feature can be handy to screen the effect of global variables within a method, however, shadowing class variables can cause surprising behavior and hard-to-spot bugs. This is particularly the case for the less seasoned Python developers.

Remediation
Depending on the intention of the developer, one possible solution would be to assign the respective values to the class variable (A.x = value, where A is the class) instead of the shadowing instance variable (a.x = value, where a = A()). Otherwise refactoring of the code should be considered.

Violation Code Sample

class A:
    x = True
    def __init__(self):
        if self.x:             # access to class variable
            self.x = False     # self.x refers to an instance variable that shadows A.x
            ...

Fixed Code Sample

class A:
    x = True
    def __init__(self):
        if self.x:
            A.x = False      # assignment to the class variable
            ...

https://stackoverflow.com/questions/43186844/python-static-class-variables/43200798#43200798 https://stackoverflow.com/questions/68645/are-static-class-variables-possible https://stackoverflow.com/questions/19902127/what-is-the-pythonic-way-to-avoid-shadowing-variables