Filter with an AST

filter.py

import operator


class InvalidFilter(Exception):
    pass


class Filter(object):
    binary_operators = {
        u"=": operator.eq,
        u"==": operator.eq,
        u"eq": operator.eq,

        u"<": operator.lt,
        u"lt": operator.lt,

        u">": operator.gt,
        u"gt": operator.gt,

        u"<=": operator.le,
        u"≤": operator.le,
        u"le": operator.le,

        u">=": operator.ge,
        u"≥": operator.ge,
        u"ge": operator.ge,

        u"!=": operator.ne,
        u"≠": operator.ne,
        u"ne": operator.ne,

        u"%": operator.mod,
        u"mod": operator.mod,

        u"+": operator.add,
        u"add": operator.add,

        u"-": operator.sub,
        u"sub": operator.sub,

        u"*": operator.mul,
        u"×": operator.mul,
        u"mul": operator.mul,

        u"/": operator.truediv,
        u"÷": operator.truediv,
        u"div": operator.truediv,

        u"**": operator.pow,
        u"^": operator.pow,
        u"pow": operator.pow,
    }

    multiple_operators = {
        u"or": any,
        u"∨": any,
        u"and": all,
        u"∧": all,
    }

    def __init__(self, tree):
        self._eval = self.build_evaluator(tree)

    def __call__(self, value):
        return self._eval(value)

    def build_evaluator(self, tree):
        try:
            operator, nodes = list(tree.items())[0]
        except Exception:
            return lambda value: tree
        try:
            op = self.multiple_operators[operator]
        except KeyError:
            try:
                op = self.binary_operators[operator]
            except KeyError:
                raise InvalidQuery("Unknown operator %s" % operator)
            return self._handle_binary_op(op, nodes)
        return self._handle_multiple_op(op, nodes)

    def _handle_multiple_op(self, op, nodes):
        elements = [self.build_evaluator(node) for node in nodes]
        return lambda value: op((e(value) for e in elements))

    def _handle_binary_op(self, op, node):
        try:
            iterator = iter(node)
        except Exception:
            return lambda value: op(value, node)
        nodes = list(iterator)
        if len(nodes) != 2:
            raise InvalidFilter(
                "Binary operator %s needs 2 arguments, %d given" %
                (op, len(nodes)))
        node0 = self.build_evaluator(node[0])
        node1 = self.build_evaluator(node[1])
        return lambda value: op(node0(value), node1(value))


f = Filter(
    {"and":
     [
         {"lt": 10},
         {"ge": 5},
     ]
})

print(f(5))
print(f(12))