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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 _browser_init(self):
 """ Init the browsing instance if not setup :rtype: None """

        if self.session:
            return

        self.session = requests.Session()
        headers = {}

        if self.user_agent:
            headers['User-agent'] = self.user_agent
        self.session.headers.update(headers)

        if self._auth_method in [None, "", "HTTPBasicAuth"]:
            if self._auth_username is not None:
                self.session.auth = (self._auth_username, self._auth_password)