Question

Is there a way to test the return of a function in a list (or dict) comprehension? I’d like to avoid writing that:

lst = []
for x in range(10):
  bar = foo(x)
  if bar:
    lst.append(bar)

and use a list comprehension instead. Obviously, I don’t want to write:

[foo(x) for x in range(10) if foo(x)]

so?

[foo(x) for x in range(10) if ??? ]

Answer 1

How about

filter(None, map(foo, range(10)))

If you don’t want to keep the intermediate list, replace map() with itertools.imap(). And with itertools.ifilter(), the whole thing could be turned into a generator.

itertools.ifilter(None, itertools.imap(foo, range(10)))