docs: def update(field, value, db, collection, match=None):
      '''
      Updates MongoDB documents.
  
      Sets ``field`` equal to ``value`` for all documents that
      meet ``match`` criteria.
  
      Arguments:
  
          field (str): Field to update.
  
          value (str): Update value.
  
          db (Database): A pymongo Database object.
  
          collection (str): Collection name.
  
          match (dict): A dictionary containing the match criteria, for example::
  
              {'seq_id': {'$in': ['a', 'b', 'c']}, 'cdr3_len': {'$gte': 18}}
      '''
      c = db[collection]
      match = match if match is not None else {}
      # check MongoDB version to use appropriate update command
      if db.client.server_info()['version'].startswith('2'):
          c.update(match, {'$set': {field: value}}, multi=True)
      else:
          c.update_many(match, {'$set': {field: value}})