add a couple of type annotations

keyring/credentials.py

@@ -1,32 +1,34 @@
 import abc
 import os
 
+from __future__ import annotations
+
 
 class Credential(metaclass=abc.ABCMeta):
     """Abstract class to manage credentials"""
 
     @abc.abstractproperty
-    def username(self):
+    def username(self) -> str | None:
         return None
 
     @abc.abstractproperty
-    def password(self):
+    def password(self) -> str | None:
         return None
 
 
 class SimpleCredential(Credential):
     """Simple credentials implementation"""
 
-    def __init__(self, username, password):
+    def __init__(self, username: str | None, password: str | None):
         self._username = username
         self._password = password
 
     @property
-    def username(self):
+    def username(self) -> str | None:
         return self._username
 
     @property
-    def password(self):
+    def password(self) -> str | None:
         return self._password
 
 
@@ -47,24 +49,24 @@ class EnvironCredential(Credential):
     False
     """
 
-    def __init__(self, user_env_var, pwd_env_var):
+    def __init__(self, user_env_var: str, pwd_env_var: str):
         self.user_env_var = user_env_var
         self.pwd_env_var = pwd_env_var
 
     def __eq__(self, other: object) -> bool:
         return vars(self) == vars(other)
 
-    def _get_env(self, env_var):
+    def _get_env(self, env_var: str) -> str:
         """Helper to read an environment variable"""
         value = os.environ.get(env_var)
         if not value:
             raise ValueError(f'Missing environment variable:{env_var}')
         return value
 
     @property
-    def username(self):
+    def username(self) -> str:
         return self._get_env(self.user_env_var)
 
     @property
-    def password(self):
+    def password(self) -> str:
         return self._get_env(self.pwd_env_var)