Question

I would like to map a method over a list of objects instantiating different classes. All the objects inherit from the same base class and define a method of the desired name.

To make it clearer consider the following code:

class A:
    def __init__(self, x):
        self.x = x

    def foo (self):
        return self.x

class B(A):
    def foo (self):
        return self.x+1

class C(A):
    def foo (self):
        return self.x-1

Now consider a list of objects instantiating the classes B and C. I would like to do something like that:

result = []
for obj in [B(1), C(1)]:
    result.append(obj.foo())

How would you proceed to map the method foo on each element of the list? Is it at all possible? The best I could come up with is something like that:

map(A.foo, [B(1), C(1)])

but clearly it doesn’t return my desired result. How can I specify the method related to the object?

I hope I made myself clear.

NB: I work primarily with Python2.7, but I would equally be interested in solutions valid for “newer” versions.

Answer 1

>>> map(lambda x: x.foo(), [B(1), C(1)])
>>> [2, 0]

The lambda function will take each object in the list and call foo() on that object. Thus the resulting list will have the results returned by the corresponding object’s foo().