yapf gbk file does not work bug?

D:>yapf d:\测试\a.py
Traceback (most recent call last):
File "c:\python27\lib\runpy.py", line 174, in run_module_as_main
"main", fname, loader, pkg_name)
File "c:\python27\lib\runpy.py", line 72, in run_code
exec code in run_globals
File "C:\Python27\Scripts\yapf.exe_main.py", line 9, in
File "c:\python27\lib\site-packages\yapf_init.py", line 313, in run_main
sys.exit(main(sys.argv))
File "c:\python27\lib\site-packages\yapf_init_.py", line 201, in main
verbose=args.verbose)
File "c:\python27\lib\site-packages\yapf_init_.py", line 251, in FormatFiles
in_place, print_diff, verify, verbose)
File "c:\python27\lib\site-packages\yapf_init_.py", line 276, in _FormatFile
logger=logging.warning)
File "c:\python27\lib\site-packages\yapf\yapflib\yapf_api.py", line 91, in FormatFile
verify=verify)
File "c:\python27\lib\site-packages\yapf\yapflib\yapf_api.py", line 154, in FormatCode
unformatted_source, reformatted_source, filename=filename)
File "c:\python27\lib\site-packages\yapf\yapflib\yapf_api.py", line 291, in _GetUnifiedDiff
lineterm='')) + '\n'
UnicodeDecodeError: 'ascii' codec can't decode byte 0xb2 in position 7: ordinal not in range(128)

D:>yapf a.py
a = 1
b = 2
c = 3

yapf‘s bug?