fix pickle load encoding between python 2 and 3 (#22621)

test=develop

python/paddle/fluid/dygraph/checkpoint.py

@@ -132,7 +132,7 @@ def load_dygraph(model_path, keep_name_table=False):
 
     with open(params_file_path, 'rb') as f:
         para_dict = pickle.load(f) if six.PY2 else pickle.load(
-            f, encoding='bytes')
+            f, encoding='latin1')
 
     if not keep_name_table and "StructuredToParameterName@@" in para_dict:
         del para_dict["StructuredToParameterName@@"]
@@ -141,6 +141,6 @@ def load_dygraph(model_path, keep_name_table=False):
     if os.path.exists(opti_file_path):
         with open(opti_file_path, 'rb') as f:
             opti_dict = pickle.load(f) if six.PY2 else pickle.load(
-                f, encoding='bytes')
+                f, encoding='latin1')
 
     return para_dict, opti_dict

python/paddle/fluid/io.py

@@ -1696,7 +1696,7 @@ def load(program, model_path, executor=None, var_list=None):
                                                    executor._default_executor)
     with open(parameter_file_name, 'rb') as f:
         load_dict = pickle.load(f) if six.PY2 else pickle.load(
-            f, encoding='bytes')
+            f, encoding='latin1')
     for v in parameter_list:
         assert v.name in load_dict, \
             "Can not find [{}] in model file [{}]".format(
@@ -1717,7 +1717,7 @@ def load(program, model_path, executor=None, var_list=None):
 
         with open(opt_file_name, 'rb') as f:
             load_dict = pickle.load(f) if six.PY2 else pickle.load(
-                f, encoding='bytes')
+                f, encoding='latin1')
         for v in optimizer_var_list:
             assert v.name in load_dict, \
                 "Can not find [{}] in model file [{}]".format(
@@ -1842,13 +1842,13 @@ def load_program_state(model_path, var_list=None):
 
     with open(parameter_file_name, 'rb') as f:
         para_dict = pickle.load(f) if six.PY2 else pickle.load(
-            f, encoding='bytes')
+            f, encoding='latin1')
 
     opt_file_name = model_prefix + ".pdopt"
     if os.path.exists(opt_file_name):
         with open(opt_file_name, 'rb') as f:
             opti_dict = pickle.load(f) if six.PY2 else pickle.load(
-                f, encoding='bytes')
+                f, encoding='latin1')
 
         para_dict.update(opti_dict)