Add new hashes introduced in Python 3.6 (#1268)

* sha3 family of hash functions
* shake variable length hashes that were introduced alongside sha3
* blake2 family of hash functions
* Mark VarLenHash as a private class, since it's not actually exported by hashlib
* Fix typos in my last, and mark hashlib.Hash as a private class since it isn't in the real hashlib

stdlib/3/hashlib.pyi

@@ -6,7 +6,7 @@ from typing import AbstractSet, Optional, Union
 
 _DataType = Union[bytes, bytearray, memoryview]
 
-class Hash(metaclass=ABCMeta):
+class _Hash(metaclass=ABCMeta):
     digest_size = ...  # type: int
     block_size = ...  # type: int
 
@@ -22,16 +22,16 @@ class Hash(metaclass=ABCMeta):
     @abstractmethod
     def hexdigest(self) -> str: ...
     @abstractmethod
-    def copy(self) -> 'Hash': ...
+    def copy(self) -> _Hash: ...
 
-def md5(arg: _DataType = ...) -> Hash: ...
-def sha1(arg: _DataType = ...) -> Hash: ...
-def sha224(arg: _DataType = ...) -> Hash: ...
-def sha256(arg: _DataType = ...) -> Hash: ...
-def sha384(arg: _DataType = ...) -> Hash: ...
-def sha512(arg: _DataType = ...) -> Hash: ...
+def md5(arg: _DataType = ...) -> _Hash: ...
+def sha1(arg: _DataType = ...) -> _Hash: ...
+def sha224(arg: _DataType = ...) -> _Hash: ...
+def sha256(arg: _DataType = ...) -> _Hash: ...
+def sha384(arg: _DataType = ...) -> _Hash: ...
+def sha512(arg: _DataType = ...) -> _Hash: ...
 
-def new(name: str, data: _DataType = ...) -> Hash: ...
+def new(name: str, data: _DataType = ...) -> _Hash: ...
 
 # New in version 3.2
 algorithms_guaranteed = ...  # type: AbstractSet[str]
@@ -40,3 +40,39 @@ algorithms_available = ...  # type: AbstractSet[str]
 # New in version 3.4
 if sys.version_info >= (3, 4):
     def pbkdf2_hmac(hash_name: str, password: _DataType, salt: _DataType, iterations: int, dklen: Optional[int] = ...) -> bytes: ...
+
+if sys.version_info >= (3, 6):
+    class _VarLenHash(metaclass=ABCMeta):
+        digest_size = ...  # type: int
+        block_size = ...  # type: int
+        name = ...  # type: str
+
+        @abstractmethod
+        def digest(self, length: int) -> bytes: ...
+        @abstractmethod
+        def hexdigest(self, length: int) -> str: ...
+        @abstractmethod
+        def update(self, arg: _DataType) -> None: ...
+        @abstractmethod
+        def copy(self) -> _VarLenHash: ...
+
+    def sha3_224(arg: _DataType = ...) -> _Hash: ...
+    def sha3_256(arg: _DataType = ...) -> _Hash: ...
+    def sha3_384(arg: _DataType = ...) -> _Hash: ...
+    def sha3_512(arg: _DataType = ...) -> _Hash: ...
+
+    def shake_128(arg: _DataType = ...) -> _VarLenHash: ...
+    def shake_256(arg: _DataType = ...) -> _VarLenHash: ...
+
+    def scrypt(password: _DataType, *, salt: _DataType, n: int, r: int, p: int, maxmem: int = ..., dklen: int = ...) -> bytes: ...
+
+    class _BlakeHash(_Hash):
+        MAX_DIGEST_SIZE = ...  # type: int
+        MAX_KEY_SIZE = ...  # type: int
+        PERSON_SIZE = ...  # type: int
+        SALT_SIZE = ...  # type: int
+
+        def __init__(self, data: _DataType, digest_size: int = ..., key: _DataType = ..., salt: _DataType = ..., person: _DataType = ..., fanout: int = ..., depth: int = ..., leaf_size: int = ..., node_offset: int = ..., node_depth: int = ..., inner_size: int = ..., last_node: bool = ...) -> None: ...
+
+    blake2b = _BlakeHash
+    blake2s = _BlakeHash