def __setitem__(self, key, value):
        if key not in self:
            super(ParamDict, self).__setitem__(key, value)
        else:
            if not isinstance(self[key], list):
                super(ParamDict, self).__setitem__(key, [self[key]])
            self[key].append(value)
If `key` is assigned more than once, `self[key]` holds a
dataset/ETHPy150Open RoseOu/flasky/venv/lib/python2.7/site-packages/httpie/input.py/ParamDict.__setitem__