input: Write a function to filter words by length.
  assert filter_by_length(['apple', 'cat', 'banana', 'dog', 'potato']) == ['apple', 'banana', 'potato']
  assert filter_by_length(['a', 'ab', 'abc', 'abcd', 'abcde', 'abcdef']) == ['abcde', 'abcdef']
  assert filter_by_length(['short', 'tiny', 'big', 'gigantic', 'small']) == ['short', 'gigantic', 'small']
output: def filter_by_length(words):
      return [word for word in words if len(word) >= 5]