python to get all files with a specified suffix under a specified path

# Get all the files in the specified path with the specified suffix.
# dir Specify the path
# ext Specify a suffix, chained lists & without dots Or don't specify. Example: ['xml', 'java']
def GetFileFromThisRootDir(dir,ext = None):
  allfiles = []
  needExtFilter = (ext != None)
  for root,dirs,files in (dir):
    for filespath in files:
      filepath = (root, filespath)
      extension = (filepath)[1][1:]
      if needExtFilter and extension in ext:
        (filepath)
      elif not needExtFilter:
        (filepath)
  return allfiles