'Create an API version request object.
:param version_string: String representation of APIVersionRequest.
Correct format is \'X.Y\', where \'X\' and \'Y\' are int values.
None value should be used to create Null APIVersionRequest,
which is equal to 0.0'

def __init__(self, version_string=None):

    self.ver_major = 0
    self.ver_minor = 0
    if (version_string is not None):
        match = re.match('^([1-9]\\d*)\\.([1-9]\\d*|0)$', version_string)
        if match:
            self.ver_major = int(match.group(1))
            self.ver_minor = int(match.group(2))
        else:
            raise exception.InvalidAPIVersionString(version=version_string)
