code: def _check_one_file(filename, formatted):
      with open(filename, "rb") as reader:
          original = reader.read()
  
      if formatted != original:
          # Run the equivalent of diff -u
          diff = list(
              difflib.unified_diff(
                  original.decode("utf8").splitlines(True),
                  formatted.decode("utf8").splitlines(True),
                  fromfile=filename,
                  tofile="{} (after clang format)".format(filename),
              )
          )
      else:
          diff = None
  
      return filename, diff
  
file_path: arrow/cpp/build-support/run_clang_format.py
imports: from __future__ import print_function
  import lintutils
  from subprocess import PIPE
  import argparse
  import difflib
  import multiprocessing
  import sys
  from functools import partial
label_desc: Use image node_id 1 for calling a global function with example usage: _check_one_file(filename, formatted) and returns: filename,  diff