Episode Details

This story was originally published on HackerNoon at: https://hackernoon.com/why-doesnt-create-independent-nested-lists-in-python-the-hidden-list-multiplication-trap.
Learn why [[0,0,0]] * 3 in Python secretly shares one list across all rows, and how to build truly independent nested lists the right way.
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[x] * n does not create n independent copies of x. It creates one object and repeats a reference to that same object n times. For immutable elements like numbers or strings, this is harmless because any "change" actually rebinds the slot to a new object. For mutable elements like lists or dicts, every slot points to the exact same object, so mutating one slot mutates all of them. The fix is to use a list comprehension — [x for _ in range(n)] — which creates a genuinely new object on each iteration. Key takeaway: * repeats references, not values.