As pointed out in the PyCharm docs, a (legacy, pre-PEP-484) way of doing this is using square brackets:

list[Foo]: List of Foo elements

dict[Foo, Bar]: Dict from Foo to Bar

list of str, as suggested in the accepted answer, does not work as expected in PyCharm.

Starting with Python 3.5 and the implementation of PEP-484, you can also use type hints, which may be nicely supported by your IDE/editor. How this is easily done in PyCharm is explained here.

In essence, to declare a list return type using type-hinting (Python >=3.5), you may do something like this:

from typing import List

"""
Great foo function.

:rtype: list[str]
"""
def foo() -> List[str]:
    return ['some string', 'some other string']

Here we declare (somewhat redundantly) that the function foo returns a list of strings, both in the type hint -> List[str] and in the docstring :rtype: list[str].

Other pre-declared types and more info can be found in the Python docs for typing.