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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 _parse_recipients(self, to):
 """Make sure we have a "," separated list of recipients :param to: Recipient(s) :type to: (str, list, :class:`pyfilemail.Contact`, :class:`pyfilemail.Group` ) :rtype: ``str`` """


        if to is None:
            return None

        if isinstance(to, list):
            recipients = []

            for recipient in to:
                if isinstance(recipient, dict):
                    if 'contactgroupname' in recipient:
                        recipients.append(recipient['contactgroupname'])

                    else:
                        recipients.append(recipient.get('email'))

                else:
                    recipients.append(recipient)

        elif isinstance(to, basestring):
            if ',' in to:
                recipients = to.strip().split(',')

            else:
                recipients = [to]

        return ', '.join(recipients)