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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 cmd_ip_counter(self):
 """Reports a breakdown of how many requests have been made per IP. .. note:: To enable this command requests need to provide a header with the forwarded IP (usually X-Forwarded-For) and be it the only header being captured. """

        ip_counter = defaultdict(int)
        for line in self._valid_lines:
            ip = line.get_ip()
            if ip is not None:
                ip_counter[ip] += 1
        return ip_counter