'Returns the value of a single variable. Wrapper around
``distutils.sysconfig.get_config_var()``.'

def get_config_var(self, key):

    cmd = 'from    distutils.sysconfig    import    get_config_var;    '
    cmd += self.print_string("get_config_var('{0}')".format(key))
    return self.command('-c', cmd, output=str).strip()
