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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 _get_process_cwd(pid):
 """ Returns the working directory for the provided process identifier. `pid` System process identifier. Returns string or ``None``. Note this is used as a workaround, since `psutil` isn't consistent on being able to provide this path in all cases, especially MacOS X. """


    cmd = 'lsof -a -p {0} -d cwd -Fn'.format(pid)

    data = common.shell_process(cmd)

    if not data is None:
        lines = str(data).split('\n')

        # the cwd is the second line with 'n' prefix removed from value
        if len(lines) > 1:
            return lines[1][1:] or None

    return None