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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 ua_string(praw_info):
 """Return the user-agent string. The user-agent string contains PRAW version and platform version info. """

        if os.environ.get('SERVER_SOFTWARE') is not None:
            # Google App Engine information
            # https://developers.google.com/appengine/docs/python/
            info = os.environ.get('SERVER_SOFTWARE')
        else:
            # Standard platform information
            info = platform.platform(True).encode('ascii', 'ignore')

        return '{0} PRAW/{1} Python/{2} {3}'.format(
            praw_info, __version__, sys.version.split()[0], info)