<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_pyof_version(module_fullname):
 """Get the module pyof version based on the module fullname. Args: module_fullname (str):
 The fullname of the module (e.g.: pyof.v0x01.common.header) Returns: str: openflow version. The openflow version, on the format 'v0x0?' if any. Or None if there isn't a version on the fullname. """

        ver_module_re = re.compile(r'(pyof\.)(v0x\d+)(\..*)')
        matched = ver_module_re.match(module_fullname)
        if matched:
            version = matched.group(2)
            return version
        return None