join() and split()

What this problem practises

Python strings are immutable sequences. "Fixing" a string always produces a new one, so the return value has to be captured; slicing rules apply, and every method — upper(), strip(), split(), join() — behaves differently from the in-place mutation you might be picturing.

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

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:

sentence = "I love Python programming"
words = sentence.split()
print(len(words))
print("-".join(words))

More strings problems

• zip() combining two lists medium
• Mixing text and numbers in print easy
• String startswith and endswith easy

Keep going

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