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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 _is_valid_channel(self, channel, conda_url='https://conda.anaconda.org'):
 """Callback for is_valid_channel."""

        if channel.startswith('https://') or channel.startswith('http://'):
            url = channel
        else:
            url = "{0}/{1}".format(conda_url, channel)

        if url[-1] == '/':
            url = url[:-1]

        plat = self._conda_api.get_platform()
        repodata_url = "{0}/{1}/{2}".format(url, plat, 'repodata.json')

        try:
            r = requests.head(repodata_url, proxies=self.proxy_servers)
            value = r.status_code in [200]
        except Exception as error:
            logger.error(str(error))
            value = False

        return value