[Dy2stat] change deprecated imp dependency to importlib, test=develop (#26453)

As the title

python/paddle/fluid/dygraph/dygraph_to_static/utils.py

@@ -19,7 +19,6 @@ import astor
 import atexit
 import copy
 import gast
-import imp
 import inspect
 import os
 import six
@@ -28,6 +27,12 @@ import textwrap
 
 from paddle.fluid import unique_name
 
+# imp is deprecated in python3
+if six.PY2:
+    import imp
+else:
+    from importlib.machinery import SourceFileLoader
+
 dygraph_class_to_static_api = {
     "CosineDecay": "cosine_decay",
     "ExponentialDecay": "exponential_decay",
@@ -391,7 +396,10 @@ def ast_to_func(ast_root, dyfunc, delete_on_exit=True):
         atexit.register(lambda: remove_if_exit(f.name))
         atexit.register(lambda: remove_if_exit(f.name[:-3] + ".pyc"))
 
+    if six.PY2:
         module = imp.load_source(module_name, f.name)
+    else:
+        module = SourceFileLoader(module_name, f.name).load_module()
     func_name = dyfunc.__name__
     if not hasattr(module, func_name):
         raise ValueError(