>>> currf = '\xe1\x84\x92\xe1\x85\xa7\xe1\x86\xab\xe1\x84\x89\xe1\x85\xb5\xe1\x84\x8b\xe1\x85\xa7\xe1\x86\xab 2\xe1\x84\x80\xe1\x85\xb5 03.avi'
>>> files = [f for f in os.listdir('.') if f.split('.')[-1] == currf.split('.')[-1]]
>>> maxcommon = max(len(os.path.commonprefix([f, fnp])) for fnp in files if fnp != f)
>>> prefix = currf[:maxcommon-1]
>>> next = min(fnp for fnp in files if fnp[:maxcommon-1] == prefix and fnp > currf)
>>> prev = max(fnp for fnp in files if fnp[:maxcommon-1] == prefix and fnp < currf)
>>> print currf
현시연 2기 03.avi
>>> print next
현시연 2기 04.avi
>>> print prev
현시연 2기 01.avi