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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_cmd(cmd):
 """Retrieve required commands for running THetA with our local bcbio python. """

    check_cmd = "RunTHetA.py"
    try:
        local_cmd = subprocess.check_output(["which", check_cmd]).strip()
    except subprocess.CalledProcessError:
        return None
    return [sys.executable, "%s/%s" % (os.path.dirname(os.path.realpath(local_cmd)), cmd)]