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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_running(self):
 """Check if ZAP is running."""

        try:
            result = requests.get(self.proxy_url)
        except RequestException:
            return False

        if 'ZAP-Header' in result.headers.get('Access-Control-Allow-Headers', []):
            return True

        raise ZAPError('Another process is listening on {0}'.format(self.proxy_url))