Use a dict to handle next scopes

Author: nicoddemus

src/_pytest/fixtures.py

@@ -451,7 +451,7 @@ def __init__(self, pyfuncitem, *, _ispytest: bool = False) -> None:
 
     @property
     def scope(self) -> "_ScopeName":
-        """Backward-compatibility to return the scope string value."""
+        """Scope string, one of "function", "class", "module", "package", "session"."""
         return self._scope.value  # type:ignore[return-value]
 
     @property
@@ -1013,7 +1013,7 @@ def __init__(
 
     @property
     def scope(self) -> "_ScopeName":
-        """Backward-compatibility to return the scope string value."""
+        """Scope string, one of "function", "class", "module", "package", "session"."""
         return self._scope.value  # type:ignore[return-value]
 
     def addfinalizer(self, finalizer: Callable[[], object]) -> None:

src/_pytest/scope.py

@@ -33,7 +33,7 @@ def index(self) -> int:
 
     def next(self) -> "Scope":
         """Return the next scope (from top to bottom)."""
-        return _next_scope(self)
+        return _NEXT_SCOPES[self]
 
     @classmethod
     def from_user(
@@ -61,19 +61,18 @@ def from_user(
 # Ordered list of scopes which can contain many tests (in practice all except Function).
 HIGH_SCOPES = [x for x in Scope if x is not Scope.Function]
 
+# Maps a high-level scope to its next scope. Function is absent here because it
+# is the bottom-most scope.
+_NEXT_SCOPES = {
+    Scope.Session: Scope.Package,
+    Scope.Package: Scope.Module,
+    Scope.Module: Scope.Class,
+    Scope.Class: Scope.Function,
+}
+
 
 @lru_cache(maxsize=None)
 def _scope_to_index(scope: Scope) -> int:
     """Implementation of Scope.index() as a free function so we can cache it."""
     scopes = list(Scope)
     return scopes.index(scope)
-
-
-@lru_cache(maxsize=None)
-def _next_scope(scope: Scope) -> Scope:
-    """Implementation of Scope.next() as a free function so we can cache it."""
-    if scope is Scope.Function:
-        raise ValueError("Function is the bottom scope")
-    scopes = list(Scope)
-    index = scopes.index(scope)
-    return scopes[index + 1]

testing/test_scope.py

@@ -18,7 +18,7 @@ def test_next() -> None:
     assert Scope.Module.next() is Scope.Class
     assert Scope.Class.next() is Scope.Function
 
-    with pytest.raises(ValueError):
+    with pytest.raises(KeyError):
         Scope.Function.next()