Generator multiples of 2

What this problem practises

Generators produce values lazily and can be consumed exactly once. That makes them memory-friendly for big sequences, and genuinely confusing the first time one is iterated again and yields nothing.

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.

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:

gen = (x * 2 for x in range(5))
print(list(gen))

More problems

• Generator multiples of 3 medium
• Checking membership in a list easy
• List methods in sequence easy

Keep going

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