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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 _update_submodules(repo_dir):
 """update submodules in a repo"""

    subprocess.check_call("git submodule init", cwd=repo_dir, shell=True)
    subprocess.check_call(
        "git submodule update --recursive", cwd=repo_dir, shell=True)