Summing dictionary values

What this problem practises

Dictionaries fail loudly on a missing key with KeyError, quietly through get(), and in genuinely surprising ways when you modify a dict while iterating it or rely on a duplicate key silently replacing the earlier entry.

This is an output-prediction problem: read the snippet carefully and write down exactly what it prints before anything runs. These questions are interview staples because they test whether you know the language rules, or merely recognise their syntax.

Difficulty: medium — expect to hold two interacting rules in your head at once, such as a boundary combined with a mutation.

The challenge

What will this program print? Type the exact output (both lines).

The code runs in PyDebug’s in-browser compiler. Open the problem, run the snippet, watch the exact error or output, and keep iterating until it is right. Signed-in solves count toward XP and your daily streak.

The snippet

The interactive editor pre-fills exactly this code — read it, then submit your prediction:

marks = {'a': 12, 'b': 10, 'c': 19}
total = 0
for k in marks:
    total += marks[k]
print(total)
print(sorted(marks))

More dictionaries problems

• KeyError: wrong dictionary key medium
• Dictionary lookup with default easy
• KeyError: pop('laxmi') missing medium

Keep going

• Output-prediction strategies — how to predict tricky snippets without running them.
• Browse every dictionaries problem in this topic.
• Common Python errors and what they actually mean, plus the Python glossary for any term used on this page.