suppose I have a class:
class Cat:
def __init__(self, name = "default", age = 0):
self.name = name
self.age = age
I also have a list of Cats:
l = [Cat('Joe')]
Now I can't call the following:
if 'Joe' in l: # the right syntax would be if Cat('Joe') in list
Which operator do I need to overload to be able to identify objects of class Cat by their member variable name?
You have to define the __eq__ method, as shown below:
class Cat:
def __init__(self, name = "default", age = 0):
self.name = name
self.age = age
def __eq__(self, other):
if isinstance(other, str):
return self.name == other
elif isinstance(other, Cat):
return self.name == other.name
So that when you run your check:
l = [Cat('Joe')]
'Joe' in l
#True
__hash__() as well so that it works with sets/dicts. See the data model documentation.
isinstance checks if other is a string (str) or another Cat, to tell __eq__ what to do in each case...for catname in l: print catname What would it print the object of class Cat or only the name of the object?__str__() as explained here__contains__ on list objects is implemented by checking for equality, so override __eq__:
class Cat:
def __init__(self, name = "default", age = 0):
self.name = name
self.age = age
def __eq__(self, other):
return self.name == other
This works irrespective of ordering because equality checking swaps its arguments when the left side does not support the operation.
If you want it to work with hash-based containers (e.g. set, dict) you'll have to override __hash__ as well:
def __hash__(self):
return hash(self.name)
__eq__(self, other): #todo check if other is ame type and if name matches self.nameDefines behavior for the equality operator, ==. Sorry, I am a C# guy...