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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 versionstring():
    # type: () -> Text
    '''
    version of CWLtool used to execute the workflow.
    '''
    pkg = pkg_resources.require("cwltool")
    if pkg:
        return u"%s %s" % (sys.argv[0], pkg[0].version)
    return u"%s %s" % (sys.argv[0], "unknown version")