Replace Python 2 type hints with real type annotations (#559)

* Replace Python 2 type hints with real type annotations

Author: dbieber

CONTRIBUTING.md

@@ -40,12 +40,9 @@ In addition, the project follows a convention of:
 - Maximum line length: 80 characters
 - Indentation: 2 spaces (4 for line continuation)
 - PascalCase for function and method names.
-- No type hints, as described in [PEP 484], to maintain compatibility with
-Python versions < 3.5.
 - Single quotes around strings, three double quotes around docstrings.
 
 [Google Python Style Guide]: http://google.github.io/styleguide/pyguide.html
-[PEP 484]: https://www.python.org/dev/peps/pep-0484
 
 ## Testing
 

fire/decorators.py

@@ -18,6 +18,7 @@
 command line arguments to client code.
 """
 
+from typing import Any, Dict
 import inspect
 
 FIRE_METADATA = 'FIRE_METADATA'
@@ -80,8 +81,7 @@ def _SetMetadata(fn, attribute, value):
   setattr(fn, FIRE_METADATA, metadata)
 
 
-def GetMetadata(fn):
-  # type: (...) -> dict
+def GetMetadata(fn) -> Dict[str, Any]:
   """Gets metadata attached to the function `fn` as an attribute.
 
   Args:
@@ -104,8 +104,7 @@ def GetMetadata(fn):
     return default
 
 
-def GetParseFns(fn):
-  # type: (...) -> dict
+def GetParseFns(fn) -> Dict[str, Any]:
   metadata = GetMetadata(fn)
   default = {'default': None, 'positional': [], 'named': {}}
   return metadata.get(FIRE_PARSE_FNS, default)