[BugFix] fix cuda-python requirement (#5261)

* fix cuda-python requirement

* update

* fix

fastdeploy/eplb/async_expert_loader.py

@@ -22,7 +22,11 @@ from typing import List, Tuple
 
 import numpy as np
 import paddle
-from cuda import cudart
+
+try:
+    from cuda import cudart
+except ImportError:
+    cudart = None
 
 from fastdeploy.config import EPLBConfig
 
@@ -90,6 +94,12 @@ def create_mmap(model_name: List, ep_rank: int, ep_size: int, shm_uuid: str, epl
         shm_ptr = ctypes.cast(shm_ptr, ctypes.POINTER(ctypes.c_int8))
         addr = ctypes.addressof(shm_ptr.contents)
 
+        if cudart is None:
+            raise ImportError(
+                "cuda-python not installed. Install the version matching your CUDA toolkit:\n"
+                "  CUDA 12.x → pip install cuda-python==12.*\n"
+            )
+
         # Register memory with CUDA
         (ret,) = cudart.cudaHostRegister(addr, shm_size, 0)
         if ret != cudart.cudaError_t.cudaSuccess: