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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def list_docs(self, options=None):
 """Return list of previously created documents."""

        if options is None:
            raise ValueError("Please pass in an options dict")

        default_options = {
            "page": 1,
            "per_page": 100,
            "raise_exception_on_failure": False,
            "user_credentials": self.api_key,
        }
        options = dict(list(default_options.items()) + list(options.items()))
        raise_exception_on_failure = options.pop("raise_exception_on_failure")

        resp = requests.get(
            "%sdocs" % (self._url), params=options, timeout=self._timeout
        )

        if raise_exception_on_failure and resp.status_code != 200:
            raise DocumentListingFailure(resp.content, resp.status_code)
        return resp