Move class-specific behaviors into the classes.

keyring/cli.py

@@ -132,20 +132,11 @@ def do_get(self):
         getattr(self, f'_emit_{self.output_format}')(credential)
 
     def _emit_json(self, credential: credentials.Credential):
-        if isinstance(credential, credentials.AnonymousCredential):
-            print(json.dumps(dict(password=credential.password)))
-            return
-        print(
-            json.dumps(dict(username=credential.username, password=credential.password))
-        )
+        print(json.dumps(credential._vars()))
 
     def _emit_plain(self, credential: credentials.Credential):
-        if (
-            not isinstance(credential, credentials.AnonymousCredential)
-            and credential.username
-        ):
-            print(credential.username)
-        print(credential.password)
+        for val in credential._vars().values():
+            print(val)
 
     def _get_creds(self) -> credentials.Credential | None:
         return get_credential(self.service, self.username)

keyring/credentials.py

@@ -13,6 +13,9 @@ def username(self) -> str: ...
     @abc.abstractproperty
     def password(self) -> str: ...
 
+    def _vars(self) -> dict[str, str]:
+        return dict(username=self.username, password=self.password)
+
 
 class SimpleCredential(Credential):
     """Simple credentials implementation"""
@@ -38,6 +41,9 @@ def __init__(self, password: str):
     def username(self) -> str:
         raise ValueError("Anonymous credential has no username")
 
+    def _vars(self) -> dict[str, str]:
+        return dict(password=self.password)
+
 
 class EnvironCredential(Credential):
     """