Appending values to a tuple

Question

This code appends a new value directly to a tuple. But, tuples are supposed to be nonchangeable. Could someone explain what is happening here?

word_frequency = [('hello', 1), ('my', 1), ('name', 2),
('is', 1), ('what', 1), ('?', 1)]

def frequency_to_words(word_frequency):
  frequency2words = {}
  for word, frequency in word_frequency:
    if frequency in frequency2words:
      frequency2words[frequency].append(word)
    else:
      frequency2words[frequency] = [word]
  return frequency2words

print(frequency_to_words(word_frequency))

Result: {1: ['hello', 'my', 'is', 'what', '?'], 2: ['name']}

Answer 1

The .append() operation is done on the list values in the frequency2words dictionary, not the tuples in word_frequency.

You can rewrite your code to be more concise using .setdefault(), which should also make it more clear what you're appending to.

def frequency_to_words(word_frequency):
  frequency2words = {}
  for word, frequency in word_frequency:
      frequency2words.setdefault(frequency, []).append(word)
  return frequency2words