def __call__(self, value):
        transform = lambda s: self.cast(s.strip(self.strip))

        splitter = shlex(value, posix=True)
        splitter.whitespace = self.delimiter
        splitter.whitespace_split = True

        return [transform(s) for s in splitter]
The actual transformation
dataset/ETHPy150Open henriquebastos/python-decouple/decouple.py/Csv.__call__