def append(self, key, value):
        """
        If a header with the given name already exists, the value is
        normally appended to the existing value separated by a comma.

        If, however, the already existing entry associated key with a
        value of type list (as is the case for "Set-Cookie"),
        the new value is appended to that list.
        """
        if key not in self:
            if key.lower() == "set-cookie":
                self[key] = [value]
            else:
                self[key] = value
        else:
            if isinstance(self[key], list):
                self[key].append(value)
            else:
                self[key] = ", ".join([self[key], value])
dataset/ETHPy150Open circuits/circuits/circuits/web/headers.py/Headers.append/original