docs(mge/serilize): enhance megengine save and load docstring

GitOrigin-RevId: f6b47a320bd46d92471f303218318a5ce8147550

imperative/python/megengine/serialization.py

@@ -8,12 +8,51 @@ from .utils.max_recursion_limit import max_recursion_limit
 
 def save(obj, f, pickle_module=pickle, pickle_protocol=pickle.DEFAULT_PROTOCOL):
     r"""Save an object to disk file.
+    The saved object must be a :class:`~.module.Module`,
+    :attr:`.Module.state_dict` or :attr:`.Optimizer.state_dict`.
+    See :ref:`serialization-guide` for more details.
 
     Args:
-        obj: object to save. Only ``module`` or ``state_dict`` are allowed.
+        obj: object to be saved.
         f: a string of file name or a text file object to which ``obj`` is saved to.
-        pickle_module: Default: ``pickle``.
-        pickle_protocol: Default: ``pickle.DEFAULT_PROTOCOL``.
+        pickle_module: the module to use for pickling.
+        pickle_protocol: the protocol to use for pickling.
+
+    .. admonition:: If you are using MegEngine with different Python versions
+       :class: warning
+
+       Different Python version may use different DEFAULT/HIGHEST pickle protocol.
+       If you want to :func:`~megengine.load` the saved object in another Python version,
+       please make sure you have used the same protocol.
+
+    .. admonition:: You can select to use ``pickle`` module directly
+
+        This interface is a wrapper of :func:`pickle.dump`. If you want to use ``pickle``,
+        See :py:mod:`pickle` for more information about how to set ``pickle_protocol``:
+
+        * :py:data:`pickle.HIGHEST_PROTOCOL` - the highest protocol version available.
+        * :py:data:`pickle.DEFAULT_PROTOCOL` - the default protocol version used for pickling.
+
+    Examples:
+
+        If you want to save object in a higher protocol version which current version Python
+        not support, you can install other pickle module instead of the build-in one.
+        Take ``pickle5`` as an example:
+
+        >>> import pickle5 as pickle  # doctest: +SKIP
+
+        It's a backport of the pickle 5 protocol (PEP 574) and other pickle changes.
+        So you can use it to save object in pickle 5 protocol and load it in Python 3.8+.
+
+        Or you can use ``pickle5`` in this way (only used with this interface)：
+
+        .. code-block:: python
+
+           import pickle5
+           import megengine
+
+           megengine.save(obj, f, pickle_module=pickle5, pickle_protocol=5)
+
     """
     if isinstance(f, str):
         with open(f, "wb") as fout:
@@ -70,30 +109,67 @@ def _get_callable_map_location(map_location):
 
 
 def load(f, map_location=None, pickle_module=pickle):
-    r"""Load an object saved with :func:~.megengine.save` from a file.
+    r"""Load an object saved with :func:`~.megengine.save` from a file.
 
     Args:
         f: a string of file name or a text file object from which to load.
-        map_location: Default: ``None``.
-        pickle_module: Default: ``pickle``.
+        map_location: defines device mapping. See examples for usage.
+        pickle_module: the module to use for pickling.
 
     Note:
-       * ``map_location`` defines device mapping. See examples for usage.
-       * If you will call :func:`~.megengine.set_default_device()`, please do it
-         before :func:`~.megengine.load()`.
+       
+        If you will call :func:`~.megengine.set_default_device()`, please do it
+        before :func:`~.megengine.load()`.
+
+    .. admonition:: If you are using MegEngine with different Python versions
+       :class: warning
+
+       Different Python version may use different DEFAULT/HIGHEST pickle protocol.
+       If you want to :func:`~megengine.load` the saved object in another Python version,
+       please make sure you have used the same protocol.
+
+    .. admonition:: You can select to use ``pickle`` module directly
+
+        This interface is a wrapper of :func:`pickle.load`. If you want to use ``pickle``,
+        See :py:mod:`pickle` for more information about how to set ``pickle_protocol``:
+
+        * :py:data:`pickle.HIGHEST_PROTOCOL` - the highest protocol version available.
+        * :py:data:`pickle.DEFAULT_PROTOCOL` - the default protocol version used for pickling.
 
     Examples:
+
+        This example shows how to load tenors to different devices:
+
         .. code-block::
 
            import megengine as mge
+
            # Load tensors to the same device as defined in model.pkl
            mge.load('model.pkl')
+
            # Load all tensors to gpu0.
            mge.load('model.pkl', map_location='gpu0')
+
            # Load all tensors originally on gpu0 to cpu0
            mge.load('model.pkl', map_location={'gpu0':'cpu0'})
+
            # Load all tensors to cpu0
            mge.load('model.pkl', map_location=lambda dev: 'cpu0')
+
+        If you are using a lower version of Python (<3.8),
+        you can use other pickle module like ``pickle5`` to load object saved in pickle 5 protocol:
+
+        >>> import pickle5 as pickle  # doctest: +SKIP
+
+        Or you can use ``pickle5`` in this way (only used with this interface)：
+
+        .. code-block:: python
+
+           import pickle5
+           import megengine
+
+           megengine.load(obj, pickle_module=pickle5)
+
     """
     if isinstance(f, str):
         with open(f, "rb") as fin: