Question

I need to do something that is functionally equivalent to this:

for foo in foos:
    bar = foo.get_bar()
    # Do something with bar

My first instinct was to use map, but this did not work:

for bar in map(get_bar, foos):
    # Do something with bar

Is what I’m trying to accomplish possible with map? Do I need to use a list comprehension instead? What is the most Pythonic idiom for this?

Answer 1

Either with lambda:

for bar in map(lambda foo: foo.get_bar(), foos):

Or simply with instance method reference on your instance’s class:

for bar in map(Foo.get_bar, foos):

As this was added from a comment, I would like to note that this requires the items of foos to be instances of Foo (i.e. all(isinstance(foo, Foo) for foo in foos) must be true) and not only as the other options do instances of classes with a get_bar method. This alone might be reason enough to not include it here.

Or with methodcaller:

import operator
get_bar = operator.methodcaller('get_bar')
for bar in map(get_bar, foos):

Or with a generator expression:

for bar in (foo.get_bar() for foo in foos):