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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_user_agent():
 """ Construct and informative user-agent string. Includes OS version and docker version info Not thread-safe :return: """


    global user_agent_string
    if user_agent_string is None:
        # get OS type
        try:
            sysinfo = subprocess.check_output('lsb_release -i -r -s'.split(' '))
            dockerinfo = subprocess.check_output('docker --version'.split(' '))

            user_agent_string = ' '.join([sysinfo.replace('\t','/'),
                                          dockerinfo.replace(" version ", "/").replace(", ", "/").replace(' ', '/')]).replace('\n','')
        except:
            user_agent_string = None

    return user_agent_string