from unittest import TestCase

import json

class JSONTestObject:

    pass

class RecursiveJSONEncoder(json.JSONEncoder):

    recurse = False

    def default(self, o):

        if o is JSONTestObject:

            if self.recurse:

                return [JSONTestObject]

            else:

                return 'JSONTestObject'

        return json.JSONEncoder.default(o)

class TestRecursion(TestCase):

    def test_listrecursion(self):

        x = []

        x.append(x)

        try:

            json.dumps(x)

        except ValueError:

            pass

        else:

            self.fail("didn't raise ValueError on list recursion")

        x = []

        y = [x]

        x.append(y)

        try:

            json.dumps(x)

        except ValueError:

            pass

        else:

            self.fail("didn't raise ValueError on alternating list recursion")

        y = []

        x = [y, y]

        # ensure that the marker is cleared

        json.dumps(x)

    def test_dictrecursion(self):

        x = {}

        x["test"] = x

        try:

            json.dumps(x)

        except ValueError:

            pass

        else:

            self.fail("didn't raise ValueError on dict recursion")

        x = {}

        y = {"a": x, "b": x}

        # ensure that the marker is cleared

        json.dumps(x)

    def test_defaultrecursion(self):

        enc = RecursiveJSONEncoder()

        self.assertEquals(enc.encode(JSONTestObject), '"JSONTestObject"')

        enc.recurse = True

        try:

            enc.encode(JSONTestObject)

        except ValueError:

            pass

        else:

            self.fail("didn't raise ValueError on default recursion")