Enable mypy's `warn_no_return` lint

pyproject.toml

@@ -156,17 +156,12 @@ lines-after-imports = 2
 [tool.mypy]
 python_version = "3.10"
 ignore_missing_imports = true
-no_implicit_optional = true
-check_untyped_defs = false
 strict_equality = true
 warn_redundant_casts = true
 warn_unused_configs = true
 warn_unused_ignores = true
 warn_return_any = true
-warn_no_return = false
 warn_unreachable = true
-show_error_codes = true
-allow_redefinition = false
 files = ["pytensor", "tests"]
 plugins = ["numpy.typing.mypy_plugin"]
 

pytensor/graph/basic.py

@@ -909,6 +909,7 @@ def ancestors(
     def expand(r: Variable) -> Iterator[Variable] | None:
         if r.owner and (not blockers or r not in blockers):
             return reversed(r.owner.inputs)
+        return None
 
     yield from cast(Generator[Variable, None, None], walk(graphs, expand, False))
 
@@ -1011,6 +1012,7 @@ def vars_between(
     def expand(r: Variable) -> Iterable[Variable] | None:
         if r.owner and r not in ins:
             return reversed(r.owner.inputs + r.owner.outputs)
+        return None
 
     yield from cast(Generator[Variable, None, None], walk(outs, expand))
 
@@ -2039,7 +2041,9 @@ def get_var_by_name(
     from pytensor.graph.op import HasInnerGraph
 
     def expand(r) -> list[Variable] | None:
-        if r.owner:
+        if not r.owner:
+            return None
+
         res = list(r.owner.inputs)
 
         if isinstance(r.owner.op, HasInnerGraph):

pytensor/tensor/rewriting/linalg.py

@@ -355,7 +355,9 @@ def local_lift_through_linalg(
     """
 
     # TODO: Simplify this if we end up Blockwising KroneckerProduct
-    if isinstance(node.op.core_op, MatrixInverse | Cholesky | MatrixPinv):
+    if not isinstance(node.op.core_op, MatrixInverse | Cholesky | MatrixPinv):
+        return None
+
     y = node.inputs[0]
     outer_op = node.op
 
@@ -383,6 +385,7 @@ def local_lift_through_linalg(
             return [block_diag(*inner_matrices)]
         else:
             raise NotImplementedError  # pragma: no cover
+    return None
 
 
 def _find_diag_from_eye_mul(potential_mul_input):