code: def list_downloadable_sources(target_dir):
      """Returns a list of python source files is target_dir
  
      Parameters
      ----------
      target_dir : string
          path to the directory where python source file are
      Returns
      -------
      list
          list of paths to all Python source files in `target_dir`
      """
      return [
          os.path.join(target_dir, fname)
          for fname in os.listdir(target_dir)
          if fname.endswith(".py")
      ]
  
imports: from __future__ import absolute_import, division, print_function
  import os
  import zipfile
label_desc: Use image node_id 2 for calling a global function with example usage: list_downloadable_sources(target_dir) and returns: unknown