org.sonar.l10n.py.rules.python.S5722.html Maven / Gradle / Ivy
This rule raises an issue when a special method is defined with an unexpected number of parameters.
Why is this an issue?
Python allows developers to customize how code is interpreted by defining special methods (also called magic methods). For example, it is possible
to override how the multiplication operator (a * b) will apply to instances of a class by defining in this class the __mul__
and __rmul__ methods. Whenever a multiplication operation is performed with this class, the Python interpreter will call one of these
methods instead of performing the default multiplication.
Each special method expects a specific number of parameters. The Python interpreter will call these methods with those parameters. Calls to a
special method will throw a TypeError if it is defined with an incorrect number of parameters.
How to fix it
Make sure to use the same signature defined in the Python documentation for each special methods.
Code examples
Noncompliant code example
class A:
def __mul__(self, other, unexpected): # Noncompliant: too many parameters
return 42
def __add__(self): # Noncompliant: missing one parameter
return 42
A() * 3 # TypeError: __mul__() missing 1 required positional argument: 'unexpected'
A() + 3 # TypeError: __add__() takes 1 positional argument but 2 were given
Compliant solution
class A:
def __mul__(self, other):
return 42
def __add__(self, other):
return 42
A() * 3
A() + 3
Resources
Documentation
- Special method names - Python special methods
- Copy module - Documentation of
__copy__ and __deepcopy__