<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def find_observatories(self, match=None):
 """Query the LDR host for observatories. Use match to restrict returned observatories to those matching the regular expression. Example: ['AGHLT', 'G', 'GHLTV', 'GHLV', 'GHT', 'H', 'HL', 'HLT', 'L', 'T', 'V', 'Z'] ['H', 'HL', 'HLT'] @type match: L{str} @param match: name to match return observatories against @returns: L{list} of observatory prefixes """

        url = "%s/gwf.json" % _url_prefix
        response = self._requestresponse("GET", url)
        sitelist = sorted(set(decode(response.read())))
        if match:
            regmatch = re.compile(match)
            sitelist = [site for site in sitelist if regmatch.search(site)]
        return sitelist