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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 prepare_cookies(self, cookies):
 """Prepares the given HTTP cookie data. This function eventually generates a ``Cookie`` header from the given cookies using cookielib. Due to cookielib's design, the header will not be regenerated if it already exists, meaning this function can only be called once for the life of the :class:`PreparedRequest <PreparedRequest>` object. Any subsequent calls to ``prepare_cookies`` will have no actual effect, unless the "Cookie" header is removed beforehand. """

        if isinstance(cookies, cookielib.CookieJar):
            self._cookies = cookies
        else:
            self._cookies = cookiejar_from_dict(cookies)

        cookie_header = get_cookie_header(self._cookies, self)
        if cookie_header is not None:
            self.headers['Cookie'] = cookie_header