def get_vm_class_for_block_number(cls, block_number: BlockNumber) -> Type['BaseVM']:
        """
        Returns the VM class for the given block number.
        """
        if cls.vm_configuration is None:
            raise AttributeError("Chain classes must define the VMs in vm_configuration")

        validate_block_number(block_number)
        for start_block, vm_class in reversed(cls.vm_configuration):
            if block_number >= start_block:
                return vm_class
        else:
            raise VMNotFound("No vm available for block #{0}".format(block_number))
Returns the VM class for the given block number.