string replace in a file using sed in python

import subprocess

def string_replace_in_file(file_name_with_path, replacements=[]):
  '''sed runs all the replacements in a single pass'''
  
  sed_cmd = ['sed', '-i']
  for l in replacements:
    find_str = l['find'].replace('/', '\/')
    replace_str = l['replace'].replace('/', '\/')
    sed_expr = "-e s/%s/%s/g" % (find_str, replace_str)
    sed_cmd += [sed_expr]
    
  return subprocess.check_call(sed_cmd + [file_name_with_path], stderr=subprocess.STDOUT)