code: def get_source_file(filename, include_no_ext=False):
      
      filename = os.path.abspath(_path_from_filename(filename))
      base, orig_ext = os.path.splitext(filename)
      for ext in PY_SOURCE_EXTS:
          source_path = "%s.%s" % (base, ext)
          if os.path.exists(source_path):
              return source_path
      if include_no_ext and not orig_ext and os.path.exists(base):
          return base
      raise NoSourceFile(filename)
docs: given a python module's file name return the matching source file
      name (the filename will be returned identically if it's already an
      absolute path to a python source file...)
  
      :type filename: str
      :param filename: python module's file name
  
  
      :raise NoSourceFile: if no source file exists on the file system
  
      :rtype: str
      :return: the absolute path of the source file if it exists