code: def sanitize(key):
      """sanitize the given metric name or label according to Prometheus rule.
      Replace all characters other than [A-Za-z0-9_] with '_'.
      """
      return _NON_LETTERS_NOR_DIGITS_RE.sub("_", key)
  
imports: import re
  from prometheus_client import start_http_server
  from prometheus_client.core import REGISTRY, CounterMetricFamily, GaugeMetricFamily, HistogramMetricFamily, UnknownMetricFamily
  from opencensus.common.transports import sync
  from opencensus.stats import aggregation_data
  from opencensus.stats import base_exporter
  import logging
label_desc: Use image node_id 4 for calling a global function with example usage: sanitize(key) and returns: _NON_LETTERS_NOR_DIGITS_RE