>>> 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

# 使用的是 [] 而不是 (): typing.List[] 而不是 typing.List()

# 类型混合，比如返回的是 (int, None) 或者是 (int, str)，那么可以写为

# typing.Tuple[int, typing.Union[str, None]] 或者

# typing.Union[typing.Tuple[int, str], typing.Tuple[int, None]]