crypto: trivial clean-up of pw_encode/pw_decode functions

electrum/crypto.py

@@ -190,6 +190,7 @@ def _hash_password(password: Union[bytes, str], *, version: int) -> bytes:
 
 
 def pw_encode_bytes(data: bytes, password: Union[bytes, str], *, version: int) -> str:
+    """plaintext bytes -> base64 ciphertext"""
     if version not in KNOWN_PW_HASH_VERSIONS:
         raise UnexpectedPasswordHashVersion(version)
     # derive key from password
@@ -199,7 +200,9 @@ def pw_encode_bytes(data: bytes, password: Union[bytes, str], *, version: int) -
     ciphertext_b64 = base64.b64encode(ciphertext)
     return ciphertext_b64.decode('utf8')
 
+
 def pw_decode_bytes(data: str, password: Union[bytes, str], *, version: int) -> bytes:
+    """base64 ciphertext -> plaintext bytes"""
     if version not in KNOWN_PW_HASH_VERSIONS:
         raise UnexpectedPasswordHashVersion(version)
     data_bytes = bytes(base64.b64decode(data))
@@ -212,15 +215,22 @@ def pw_decode_bytes(data: str, password: Union[bytes, str], *, version: int) ->
         raise InvalidPassword() from e
     return d
 
+
 def pw_encode(data: str, password: Union[bytes, str, None], *, version: int) -> str:
+    """plaintext str -> base64 ciphertext"""
     if not password:
         return data
-    return pw_encode_bytes(to_bytes(data, "utf8"), password, version=version)
+    plaintext_bytes = to_bytes(data, "utf8")
+    return pw_encode_bytes(plaintext_bytes, password, version=version)
+
 
 def pw_decode(data: str, password: Union[bytes, str, None], *, version: int) -> str:
+    """base64 ciphertext -> plaintext str"""
     if password is None:
         return data
-    return to_string(pw_decode_bytes(data, password, version=version), "utf8")
+    plaintext_bytes = pw_decode_bytes(data, password, version=version)
+    plaintext_str = to_string(plaintext_bytes, "utf8")
+    return plaintext_str
 
 
 def sha256(x: Union[bytes, str]) -> bytes: