[Enhance] Move import yapf to function

Author: HAOCHENYE

mmengine/config/config.py

@@ -17,11 +17,9 @@
 from pathlib import Path
 from typing import Any, Optional, Sequence, Tuple, Union
 
-import yapf
 from addict import Dict
 from rich.console import Console
 from rich.text import Text
-from yapf.yapflib.yapf_api import FormatCode
 
 from mmengine.fileio import dump, load
 from mmengine.logging import print_log
@@ -1375,6 +1373,8 @@ def env_variables(self) -> dict:
     @property
     def pretty_text(self) -> str:
         """Get formatted python config text."""
+        import yapf
+        from yapf.yapflib.yapf_api import FormatCode
 
         indent = 4
 
@@ -1442,6 +1442,7 @@ def _contain_invalid_identifier(dict_str):
             return contain_invalid_identifier
 
         def _format_dict(input_dict, outest_level=False):
+
             r = ''
             s = []