punctuation mark here means just [.,] or the whole python punctuation character class:
print string.punctuation
[!"#$%&'()*+,-./:;<=>?@[]^_`{|}]

punctuation mark here means just [.,] or the whole python punctuation character class:
print string.punctuation
[!"#$%&'()*+,-./:;<=>?@[]^_`{|}]

?

One of final tests test against n = 1,234,567,890
while assumption in task description says:
Assume: 0 <= n < 1,000,000,000