Add KeyHsher class and documentation

src/datasets/keryhash.py

@@ -14,3 +14,36 @@
 # limitations under the License.
 
 # Lint as: python3
+
+"""
+Hashing function for dataset keys using `hashlib.md5`
+
+Requirements for the hash function:
+
+- Provides a uniformly distributed hash from random space
+- Adequately fast speed
+- Working with multiple input types (in this case, `str`, `int` or `bytes`)
+- Should be platform independent (generates same hash on different OS and systems)
+
+The hashing function provides a unique 128-bit integer hash of the key provided.
+
+The split name is being used here as the hash salt to avoid having same hashes
+in different splits due to same keys
+"""
+
+import hashlib
+from typing import Union
+
+class KeyHasher(object):
+    """KeyHasher class for providing hash using md5"""
+
+    def __init__(self, hash_salt: str):
+        self._split_md5 = hashlib.md5(_as_bytes(hash_salt))
+
+    def _as_bytes(self, hash_data: Union[str, int, bytes]) -> bytes:
+        """
+        Returns the input hash_data in its bytes form
+
+        Args:
+        hash_data: the hash salt/key to be converted to bytes
+        """