docs(imperative): add dlpack docstring

GitOrigin-RevId: 4898d4a4db9053d70633ae8ec8cc4c10ca9dc0c9

imperative/python/megengine/utils/__init__.py

 # -*- coding: utf-8 -*-
+from . import dlpack

imperative/python/megengine/utils/dlpack.py

-from typing import Any
-
 from ..core._imperative_rt.core2 import _from_dlpack
 
+__all__ = [
+    "to_dlpack",
+    "from_dlpack",
+]
+
 
 def to_dlpack(tensor, stream=None):
+    """
+    Encodes a megengine tensor to DLPack.
+    
+    Args:
+        tensor (Tensor): The input tensor, and the data type can be `float16`, `float32`,
+                    `int8`, `int16`, `int32`, `uint8`, `uint16`, `complex64`.
+
+        stream (Integer or None): An optional Python integer representing a CUDA stream,
+                    The current stream is synchronized with this stream before the capsule is created.
+                    If None or -1 is passed then no synchronization is performed.
+    Returns:
+        dltensor, and the data type is PyCapsule.
+
+    Examples:
+        .. code-block:: python
+
+            import megengine as mge
+            # x is a tensor with shape [2, 3]
+            x = mge.tensor([[0.2, 0.3, 0.5],
+                            [0.1, 0.2, 0.6]])
+            dlpack = mge.utils.dlpack.to_dlpack(x)
+            print(dlpack)
+            # <capsule object "dltensor" at 0x7ff04b69cc00>
+    
+    """
+
     if stream is not None and stream != -1:
         return tensor.__dlpack__(stream)
     else:
         return tensor.__dlpack__()
 
 
-def from_dlpack(ext_tensor: Any, stream=None):
+def from_dlpack(ext_tensor, stream=None):
+    """
+    Decodes a DLPack to a megengine tensor.
+
+    Args:
+        ext_tensor (PyCapsule): a PyCapsule object with the dltensor.
+
+        stream (Integer or None): An optional Python integer representing a CUDA stream,
+                    user needs to know which stream the dlpack is generated.
+                    If None then represent producers and consumers on the same stream.
+
+    Returns:
+        tensor (Tensor): a megengine tensor decoded from DLPack. 
+
+    Examples:
+        .. code-block:: python
+
+            import megengine as mge
+            # x is a tensor with shape [2, 3]
+            x = mge.tensor([[0.2, 0.3, 0.5],
+                            [0.1, 0.2, 0.6]])
+            dlpack = mge.utils.dlpack.to_dlpack(x)
+            x = mge.utils.dlpack.from_dlpack(dlpack)
+            print(x)
+            # Tensor([[0.2, 0.3, 0.5],
+            #  [0.1, 0.2, 0.6]], device=gpu0:0) 
+    """
+
     if isinstance(stream, int):
         assert stream >= 0, "device stream should be a positive value"
     stream = 0 if stream is None else stream