code: def sha1(filename):
      
      filename = unmap_file(filename)
      if filename not in file_cache:
          cache_file(filename)
          if filename not in file_cache:
              return None
          pass
      if file_cache[filename].sha1:
          return file_cache[filename].sha1.hexdigest()
      sha1 = hashlib.sha1()
      for line in file_cache[filename].lines['plain']:
          sha1.update(line.encode('utf-8'))
          pass
      file_cache[filename].sha1 = sha1
      return sha1.hexdigest()
docs: Return SHA1 of filename.