>>> def test_annotation_py2(a_str: str):
  File "<stdin>", line 1
    def test_annotation_py2(a_str: str):
                                 ^
SyntaxError: invalid syntax

>>> # all is python built-in type (single)
... def search_for(neddle: str, haystack: str) -> int:
...     offset = haystack.find(needle)
...     return offset
... 
>>> # More complicated types
... 
>>> # Python3.5 added the `typing` module, which both gives us a bunch of new names
... # for types, and tools to build our own types
... 
>>> from typing import List
>>> def multisearch(needle: str, haystack: str) -> List[int]:
...     offset = haystack.find(needle)
...     if offset == -1:
...             return []
...     else:
...             return [offset] + multisearch(needle, haystack[offset+1:])
... 
>>> # In func multisearch, we define a new type List[int], `List` is from `typeing`, `int` is python built-in type. 
# There are many of these -e.g. Dict[keytype, valuetype], if you need more, you can view `typing` documentation 
... 
>>> # A func reteurn different type, use `Union`
... 
>>> from typing import Union
>>> def search_for(needle: str, haystack: str) -> Union[int, None]:
...     offset = haystack.find(needle)
...     if offset == -1:
...             return None
...     else:
...             return offset