Fix Boolean value of Tensor ambiguity error in mistral.py (#3790)

* Fix is_contiguous() method call and remove duplicate imports

- Fix bug in rope_embedding.py where is_contiguous was used without
  parentheses, causing the method object (always truthy) to be evaluated
  instead of calling the method. This fixes issue #3781 where fast rope
  backpropagation was broken for zero strided/non-contiguous tensors.

- Remove duplicate `import torch` in rl.py (lines 20 and 25)
- Remove duplicate `import functools` and `import types` in vision.py

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Fix Boolean value of Tensor ambiguity error in mistral.py

Replace `or` operator with explicit `is None` check when getting
n_items from kwargs. The `or` operator fails when the value is a
Tensor because Python cannot determine the boolean value of a
multi-element tensor.

Fixes #3766

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Update rope_embedding.py

---------

Co-authored-by: yurekami <yurekami@users.noreply.github.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: Daniel Han <danielhanchen@gmail.com>

unsloth/models/mistral.py

@@ -307,9 +307,9 @@ def MistralForCausalLM_fast_forward(
             RETURN_LOGITS = False
 
         if not RETURN_LOGITS and labels is not None:
-            n_items = kwargs.get("num_items_in_batch", None) or kwargs.get(
-                "n_items", None
-            )
+            n_items = kwargs.get("num_items_in_batch", None)
+            if n_items is None:
+                n_items = kwargs.get("n_items", None)
             logit_softcapping = getattr(self.config, "final_logit_softcapping", 0)
 
             # loss = fused_linear_cross_entropy(
@@ -363,11 +363,13 @@ def MistralForCausalLM_fast_forward(
             shift_labels,
             kwargs.get("packed_seq_lengths"),
         )
+        n_items = kwargs.get("num_items_in_batch", None)
+        if n_items is None:
+            n_items = kwargs.get("n_items", None)
         loss = fast_cross_entropy_loss(
             logits = shift_logits,
             labels = shift_labels,
-            n_items = kwargs.get("num_items_in_batch", None)
-            or kwargs.get("n_items", None),
+            n_items = n_items,
         )
 
     if not return_dict:

unsloth/models/rl.py

@@ -22,7 +22,6 @@ from typing import Any, Callable, Dict, List, Literal, Optional, Tuple, Union
 import inspect
 import os
 import re
-import torch
 from unsloth_zoo.compiler import create_new_function
 from unsloth_zoo.log import logger
 from unsloth_zoo.logging_utils import PatchRLStatistics

unsloth/models/vision.py

@@ -68,11 +68,9 @@ import functools
 import os
 import gc
 import math
-import functools
 from typing import Optional, Tuple, List, Union
 import re, inspect, sys
 import contextlib
-import types
 
 try:
     from huggingface_hub.utils import get_token