<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_ngrams(n, text):
 """Calculates n-grams. Args: n: which n-grams to calculate text: An array of tokens Returns: A set of n-grams """

  ngram_set = set()
  text_length = len(text)
  max_index_ngram_start = text_length - n
  for i in range(max_index_ngram_start + 1):
    ngram_set.add(tuple(text[i:i + n]))
  return ngram_set