__eq__ not overridden when adding attributes¶
ID: py/missing-equals
Kind: problem
Security severity:
Severity: warning
Precision: high
Tags:
- quality
- reliability
- correctness
Query suites:
- python-security-and-quality.qls
Click to see the query in the CodeQL repository
A class that defines attributes that are not present in its superclasses may need to override the __eq__() method (__ne__() should also be defined).
Adding additional attributes without overriding __eq__() means that the additional attributes will not be accounted for in equality tests.
Recommendation¶
Override the __eq__ method.
Example¶
In the following example the ColorPoint class subclasses the Point class and adds a new attribute, but does not override the __eq__ method.
class Point(object):
def __init__(self, x, y):
self._x = x
self._y = y
def __repr__(self):
return 'Point(%r, %r)' % (self._x, self._y)
def __eq__(self, other):
if not isinstance(other, Point):
return False
return self._x == other._x and self._y == other._y
class ColorPoint(Point):
def __init__(self, x, y, color):
Point.__init__(self, x, y)
self._color = color
def __repr__(self):
return 'ColorPoint(%r, %r)' % (self._x, self._y, self._color)
#ColorPoint(0, 0, Red) == ColorPoint(0, 0, Green) should be False, but is True.
#Fixed version
class ColorPoint(Point):
def __init__(self, x, y, color):
Point.__init__(self, x, y)
self._color = color
def __repr__(self):
return 'ColorPoint(%r, %r)' % (self._x, self._y, self._color)
def __eq__(self, other):
if not isinstance(other, ColorPoint):
return False
return Point.__eq__(self, other) and self._color = other._color
References¶
Peter Grogono, Philip Santas: Equality in Object Oriented Languages