Fixed mypy again

lambeq/backend/grammar.py

@@ -280,20 +280,20 @@ def tensor(self, other: Iterable[Self]) -> Self: ...
     @overload
     def tensor(self, other: Self, *rest: Self) -> Self: ...
 
-    def tensor(self, other: Self | Iterable[Self], *rest: Self) -> Self | Any:
+    def tensor(self, other: Self | Iterable[Self], *rest: Self) -> Self:
         try:
             tys = [*other, *rest]
         except TypeError:
-            return NotImplemented
+            raise NotImplementedError
 
         # Diagrams are iterable - the identity diagram has
         # an empty list for its layers but may still contain types
         if getattr(other, 'is_id', False):
-            return NotImplemented
+            raise NotImplementedError
 
         if any(not isinstance(ty, type(self))
                or self.category != ty.category for ty in tys):
-            return NotImplemented
+            raise NotImplementedError
 
         return self._fromiter(ob for ty in (self, *tys) for ob in ty)
 
@@ -957,11 +957,11 @@ def lift(cls, diagrams: Iterable[Diagrammable | Ty]) -> list[Self]:
 
         return diags  # type: ignore[return-value]
 
-    def tensor(self, *diagrams: Diagrammable | Ty) -> Self | Any:
+    def tensor(self, *diagrams: Diagrammable | Ty) -> Self:
         try:
             diags = self.lift([self, *diagrams])
         except ValueError:
-            return NotImplemented
+            raise NotImplementedError
 
         right = dom = self.dom.tensor(*[
             diagram.to_diagram().dom for diagram in diagrams
@@ -1016,11 +1016,11 @@ def __getitem__(self, key: int | slice) -> Self:
             return self[key:key + 1]
         raise TypeError
 
-    def then(self, *diagrams: Diagrammable) -> Self | Any:
+    def then(self, *diagrams: Diagrammable) -> Self:
         try:
             diags = self.lift(diagrams)
         except ValueError:
-            return NotImplemented
+            raise NotImplementedError
 
         layers = [*self.layers]
         cod = self.cod

lambeq/backend/pennylane.py

@@ -43,7 +43,7 @@
 
 from itertools import product
 import sys
-from typing import List, TYPE_CHECKING, Union, Set, Tuple
+from typing import List, Set, Tuple, TYPE_CHECKING, Union
 
 import pennylane as qml
 import sympy

lambeq/backend/pregroup_tree.py

@@ -116,14 +116,14 @@ def __eq__(self, other: object) -> bool:
                      == (other.parent.ind if other.parent else None))
                 and self.children == other.children)
 
-    def is_same_word(self, other: object) -> bool:
+    def is_same_word(self, other: object) -> bool:  # type : [no-any-return]
         """Check if these words are the same words in the sentence.
 
         This is a relaxed version of the `__eq__` function
         which doesn't check equality of the children - essentially,
         this just checks if `other` is the same token."""
         if not isinstance(other, PregroupTreeNode):
-            return NotImplemented
+            raise NotImplementedError
         return (self.word == other.word
                 and self.ind == other.ind)