<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def preview(self):
 """Preview the purchase of this gift card"""


        if hasattr(self, '_url'):
            url = self._url + '/preview'
            return self.post(url)
        else:
            url = urljoin(recurly.base_uri(), self.collection_path + '/preview')
            return self.post(url)