def __init__(self, tree, filename):
        self._tree = tree
        self._errors = []
Returns the challenge url.
dataset/ETHPy150Open BU-NU-CLOUD-SP16/Trusted-Platform-Module-nova/nova/hacking/checks.py/BaseASTChecker.__init__--crossover with--dataset/ETHPy150Open discreteoptimization/setcover/submit.py/challenge_url