Returns the `value` of the `Category` member with the matching *name*
        or `None` if no member match.

        Example:

        >>> class Format(Category):
        ...     hour = 'hh'
        ...     minute = 'mm'
        ...     second = 'ss'
        >>> Format.get_value('hour')
        'hh'
        >>> Format.get_value('day')

def get_value(cls, name):
        """ Returns the `value` of the `Category` member with the matching *name*
        or `None` if no member match.

        Example:

        >>> class Format(Category):
        ...     hour = 'hh'
        ...     minute = 'mm'
        ...     second = 'ss'
        >>> Format.get_value('hour')
        'hh'
        >>> Format.get_value('day')

        """
        for member in cls:
            if member.name == name:
                return member.value
        return None