Magic Methods in Python can be Risky

Production RiskSoftware ResiliencyCode Reliability

Magic Methods in Python can be Risky

This code insight counts one violation each time a magic method is called, except if it is in the body of a magic method.


first_names = ["eve", "lisa", "robert", "paul", "alice"]
if first_names.__contains__("robert"):
    print("list of first names contains robert")


example 1

first_names = ["eve", "lisa", "robert", "paul", "alice"]
if "robert" in first_names:
    print("list of first names contains robert")

this example illustrate the work around for the bad example above: the __contains__ method is still called, but in background through the use of python high level mechanism, for which magic methods are intended to be used.

example 2

class child_class(parent_class):
def __init__():

def __contains__(arg1, arg2):

in this example, the call to super().__init__() and parent_class.__init__() are not violation because its a call of parent’s method in a context of respectively overriding and overloading




Why you should care

Magic methods (starting and ending with two underscores) should not have to be called directly unless you’re overriding a method of the same name. Magic methods are used to implement specific protocols and are called for you, either due to operator access or due to some special operation.

Business Impacts

Production Risk

CAST recommendations



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