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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def list_downloadable_sources(target_dir):
 """Returns a list of python source files is target_dir Parameters target_dir : str 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')]