Return the size in bits
            Return None if the size is not known
        Returns:
            int

def size(self):
        '''
            Return the size in bits
            Return None if the size is not known
        Returns:
            int
        '''
        t = self._type
        if t.startswith('uint'):
            return int(t[len('uint'):])
        if t.startswith('int'):
            return int(t[len('int'):])
        if t == 'bool':
            return int(8)
        if t == 'address':
            return int(160)
        if t.startswith('bytes'):
            return int(t[len('bytes'):])
        return None