Replace `re` with `regex` (#457)

* replace `re` with `regex`

* add regex in requirements

* use regex on windows and re on linux

* update requirements.txt

mmcv/cnn/bricks/plugin.py

 import inspect
-import re
+import platform
 
 from .registry import PLUGIN_LAYERS
 
+if platform.system() == 'Windows':
+    import regex as re
+else:
+    import re
+
 
 def infer_abbr(class_type):
     """Infer abbreviation from the class name.

mmcv/utils/config.py

@@ -2,7 +2,6 @@
 import ast
 import os.path as osp
 import platform
-import re
 import shutil
 import sys
 import tempfile
@@ -15,6 +14,11 @@ from yapf.yapflib.yapf_api import FormatCode
 
 from .path import check_file_exist
 
+if platform.system() == 'Windows':
+    import regex as re
+else:
+    import re
+
 BASE_KEY = '_base_'
 DELETE_KEY = '_delete_'
 RESERVED_KEYS = ['filename', 'text', 'pretty_text']

requirements.txt

 addict
 numpy
 pyyaml
+regex;sys_platform=='win32'
 yapf

tests/test_logging.py

 import logging
-import re
+import platform
 import tempfile
 from unittest.mock import patch
 
@@ -7,6 +7,11 @@ import pytest
 
 from mmcv import get_logger, print_log
 
+if platform.system() == 'Windows':
+    import regex as re
+else:
+    import re
+
 
 @patch('torch.distributed.get_rank', lambda: 0)
 @patch('torch.distributed.is_initialized', lambda: True)

tests/test_ops/test_syncbn.py

 import os
-import re
+import platform
 
 import numpy as np
 import torch
 import torch.distributed as dist
 import torch.nn as nn
 
+if platform.system() == 'Windows':
+    import regex as re
+else:
+    import re
+
 
 class TestSyncBN(object):