add (overwrite with) mypy stubs, if available

stdlib/3/base64.pyi

@@ -0,0 +1,25 @@
+# Stubs for base64
+
+# Based on http://docs.python.org/3.2/library/base64.html
+
+from typing import IO
+
+def b64encode(s: bytes, altchars: bytes = None) -> bytes: ...
+def b64decode(s: bytes, altchars: bytes = None,
+              validate: bool = False) -> bytes: ...
+def standard_b64encode(s: bytes) -> bytes: ...
+def standard_b64decode(s: bytes) -> bytes: ...
+def urlsafe_b64encode(s: bytes) -> bytes: ...
+def urlsafe_b64decode(s: bytes) -> bytes: ...
+def b32encode(s: bytes) -> bytes: ...
+def b32decode(s: bytes, casefold: bool = False,
+              map01: bytes = None) -> bytes: ...
+def b16encode(s: bytes) -> bytes: ...
+def b16decode(s: bytes, casefold: bool = False) -> bytes: ...
+
+def decode(input: IO[bytes], output: IO[bytes]) -> None: ...
+def decodebytes(s: bytes) -> bytes: ...
+def decodestring(s: bytes) -> bytes: ...
+def encode(input: IO[bytes], output: IO[bytes]) -> None: ...
+def encodebytes(s: bytes) -> bytes: ...
+def encodestring(s: bytes) -> bytes: ...