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)

[tomchristie]

So, at this point in the project lifespan we're very much tending towards not introducing any code changes unless clearly necessary, since they always come with potentially unexpected risks.

I'm not necessarily against this, if the pull request looked super obviously sensible, but. 🤷‍♂️