Here is my code:
class a[object]:
d='ddd'
def __contains__[self]:
if self.d:return True
b=a[]
print b.contains['d'] # error
print contains[b,'d'] # error
Chris Martin
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asked Dec 27, 2009 at 1:49
Like all special methods
[with "magic names" that begin and end in __], __contains__ is not meant to be called directly [except in very specific cases, such as up=calls to the superclass]: rather, such methods are called as part of the operation of built-ins and operators. In the case of __contains__, the operator in question is in -- the "containment check" operator.
With your
class a as you present it [except for fixing your typo, and using True instead of true!-], and b as its instance, print 'x' in b will print True -- and so will any other containment check on b, since b always returns True [because self.d, a non-empty string, is true].
answered Dec 27, 2009 at 2:04
Alex MartelliAlex Martelli
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to get your code to do something [although nothing useful]:
class a[object]:
d = 'ddd'
def __contains__[self, m]:
if self.d:
return True
b = a[]
>>> 'd' in b
True
The docs.
Julius
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answered Dec 27, 2009 at 1:51
cobbalcobbal
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__contains__ method defines how instances of class behave when they appear at right side of in and not in operator.
class Person[object]:
def __init__[self,name,age]:
self.name = name
self.age = age
def __contains__[self,param1]:
return True if param1 in self.__dict__.keys[] else False
>>> p = Person['Robby Krieger',23]
>>> 'name' in p
True
Azat Ibrakov
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answered Jan 1, 2013 at 9:33
vijay shankervijay shanker
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1
if self.d:return true
self.d is the string 'ddd'. Non-empty strings are always truthy: when you use if on 'ddd' it will always act as if you'd said if True:.
I think what you probably meant is:
def __contains__[self, item]:
return item in self.d
in is the operator that calls the __contains__ method behind the scenes.
answered Dec 27, 2009 at 1:56
bobincebobince
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Lets see a very simple example of magic method __contains__ :
Suppose I have class Player and my __init__ method takes one string argument name. In main I have created an object [obj1] of class Player.
Now if I want to know if my obj1 [in this case attribute name of obj1] contains a particular string, substring or an alphabet, I have to implement __contains__ method as shown in the example.
If my class has __contains__ method I can call built-in operator in on my custom objects as shown in the example.
class Player[]:
def __init__[self, name]:
self.name=name
def __contains__[self, substring]:
if substring in self.name:
return True
else:
return False
obj1=Player["Sam"]
print ['am' in obj1] ----> True
print ['ami' in obj1] ----> False
answered Jul 29, 2016 at 10:00
N RandhawaN Randhawa
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