Delay creation of Scan inner mode

pytensor/scan/op.py

@@ -58,7 +58,7 @@ from pytensor import tensor as pt
 from pytensor.compile.builders import construct_nominal_fgraph, infer_shape
 from pytensor.compile.function.pfunc import pfunc
 from pytensor.compile.io import In, Out
-from pytensor.compile.mode import Mode, get_default_mode, get_mode
+from pytensor.compile.mode import Mode, get_mode
 from pytensor.compile.profiling import register_profiler_printer
 from pytensor.configdefaults import config
 from pytensor.gradient import DisconnectedType, NullType, Rop, grad, grad_undefined
@@ -761,18 +761,7 @@ class Scan(Op, ScanMethodsMixin, HasInnerGraph):
         self.profile = profile
         self.allow_gc = allow_gc
         self.strict = strict
-
-        # Clone mode_instance, altering "allow_gc" for the linker,
-        # and adding a message if we profile
-        if self.name:
-            message = f"{self.name} sub profile"
-        else:
-            message = "Scan sub profile"
-
-        self.mode = get_default_mode() if mode is None else mode
-        self.mode_instance = get_mode(self.mode).clone(
-            link_kwargs=dict(allow_gc=self.allow_gc), message=message
-        )
+        self.mode = mode
 
         # build a list of output types for any Apply node using this op.
         self.output_types = []
@@ -1445,10 +1434,17 @@ class Scan(Op, ScanMethodsMixin, HasInnerGraph):
         elif self.profile:
             profile = self.profile
 
+        # Clone mode_instance, altering "allow_gc" for the linker,
+        # and adding a message if we profile
+        mode_instance = get_mode(self.mode).clone(
+            link_kwargs=dict(allow_gc=self.allow_gc),
+            message=f"{self.name or 'Scan'} sub profile",
+        )
+
         self._fn = pfunc(
             wrapped_inputs,
             wrapped_outputs,
-            mode=self.mode_instance,
+            mode=mode_instance,
             accept_inplace=False,
             profile=profile,
             on_unused_input="ignore",