pylock: remove unused attribute

Author: sbidoul

src/pip/_internal/models/pylock.py

@@ -209,7 +209,6 @@ class PylockValidationError(Exception):
 class PylockRequiredKeyError(PylockValidationError):
     def __init__(self, key: str) -> None:
         super().__init__(f"Missing required key {key!r}")
-        self.key = key
 
 
 class PylockUnsupportedVersionError(PylockValidationError):

tests/unit/test_pylock.py

@@ -75,7 +75,7 @@ def test_pylock_missing_version() -> None:
     }
     with pytest.raises(PylockRequiredKeyError) as exc_info:
         Pylock.from_dict(data)
-    assert exc_info.value.key == "lock-version"
+    assert str(exc_info.value) == "Missing required key 'lock-version'"
 
 
 def test_pylock_missing_created_by() -> None:
@@ -85,7 +85,7 @@ def test_pylock_missing_created_by() -> None:
     }
     with pytest.raises(PylockRequiredKeyError) as exc_info:
         Pylock.from_dict(data)
-    assert exc_info.value.key == "created-by"
+    assert str(exc_info.value) == "Missing required key 'created-by'"
 
 
 def test_pylock_missing_packages() -> None:
@@ -95,7 +95,7 @@ def test_pylock_missing_packages() -> None:
     }
     with pytest.raises(PylockRequiredKeyError) as exc_info:
         Pylock.from_dict(data)
-    assert exc_info.value.key == "packages"
+    assert str(exc_info.value) == "Missing required key 'packages'"
 
 
 def test_pylock_packages_without_dist() -> None: