code: def proj4_to_epsg(projection):
      
  
      def make_definition(value):
          return {x.strip().lower() for x in value.split('+') if x}
  
      # Use the EPSG in the definition if available
      match = EPSG_RE.search(projection.srs)
      if match:
          return int(match.group(1))
  
      # Otherwise, try to look up the EPSG from the pyproj data file
      pyproj_data_dir = os.path.join(os.path.dirname(pyproj.__file__), 'data')
      pyproj_epsg_file = os.path.join(pyproj_data_dir, 'epsg')
      if os.path.exists(pyproj_epsg_file):
          definition = make_definition(projection.srs)
          f = open(pyproj_epsg_file, 'r')
          for line in f.readlines():
              match = PYPROJ_EPSG_FILE_RE.search(line)
              if match:
                  file_definition = make_definition(match.group(2))
                  if definition == file_definition:
                      return int(match.group(1))
      return None
docs: Attempts to convert a PROJ4 projection object to an EPSG code and returns None if conversion fails