The SingleOperandHolder is unnecessary

[ariel-m-s]

Currently, the permissions module defines two OperandHolders, which I think is unnecessary.

django-rest-framework/rest_framework/permissions.py

Lines 11 to 47 in fd017d0

	class OperationHolderMixin:
	def __and__(self, other):
	return OperandHolder(AND, self, other)
	def __or__(self, other):
	return OperandHolder(OR, self, other)
	def __rand__(self, other):
	return OperandHolder(AND, other, self)
	def __ror__(self, other):
	return OperandHolder(OR, other, self)
	def __invert__(self):
	return SingleOperandHolder(NOT, self)
	class SingleOperandHolder(OperationHolderMixin):
	def __init__(self, operator_class, op1_class):
	self.operator_class = operator_class
	self.op1_class = op1_class
	def __call__(self, *args, **kwargs):
	op1 = self.op1_class(*args, **kwargs)
	return self.operator_class(op1)
	class OperandHolder(OperationHolderMixin):
	def __init__(self, operator_class, op1_class, op2_class):
	self.operator_class = operator_class
	self.op1_class = op1_class
	self.op2_class = op2_class
	def __call__(self, *args, **kwargs):
	op1 = self.op1_class(*args, **kwargs)
	op2 = self.op2_class(*args, **kwargs)
	return self.operator_class(op1, op2)

The SingleOperandHolder is only used for the negation operation (NOT). Instead, this could be implemented with a single class that works for all operations. I believe this implementation improves redability.

class OperationHolderMixin:
    ...
    ...

    def __invert__(self):
        return OperandHolder(NOT, self)


# A single class for an arbitrary number of operands.
class OperandHolder(OperationHolderMixin):
    def __init__(self, operator_class, *operand_classes):
        self.operator_class = operator_class
        self.operand_classes = operand_classes

    def __call__(self, *args, **kwargs):
        operands = map(lambda op: op(*args, **kwargs), self.operand_classes)
        return self.operator_class(*operands)

Originally posted by @ariel-m-s in #7914