for loops — how do they work inside?

Source code

for x in []:
    print(x)

❯ Try editing the highlighted part of the code above

Edit the [ … ] in the code above (e.g. 1, 2, 3, 4). Changing the items changes how many times next runs — and which element gets skipped at the end.

Memory / executionStep 1 / 5

👁 What you can see ── for pulls them out one at a time

for x in [10, 20, 30]: puts the list’s contents into x one at a time and prints each. The output, top to bottom, is 10, 20, 30. It’s a familiar shape ── nothing mysterious. ── But how does Python actually “take them out one at a time” inside? Use ▶ to peek step by step. At the end, a “trap” shows up that bites if you don’t know the mechanism.

for loops — how do they work inside?

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