enumerate in Python: Number Checklist Lines with start

Start with a small, explicit task

Prepare a numbered inspection checklist that begins at 7 because earlier items are shown elsewhere. Format each pair into a display line. Then check an empty checklist and a reordered copy. The item text is the data; the number belongs to this particular presentation.

Run the complete example

This original example was checked with Python 3.12.14. Save it as python_enumerate.py and run it with Python 3.12. It uses only the standard library. The assertions check the stated results.

checklist = ["Inspect seal", "Record temperature", "Store sample"]
pairs = list(enumerate(checklist, start=7))
lines = [f"{number}. {text}" for number, text in pairs]
assert pairs[0] == (7, "Inspect seal")
assert lines == ["7. Inspect seal", "8. Record temperature",
                 "9. Store sample"]
assert list(enumerate([], start=7)) == []
reordered = list(enumerate(list(reversed(checklist)), start=7))
assert reordered[0] == (7, "Store sample")
print("\n".join(lines))
print(reordered[0])

Explain the result

Each tuple contains the generated number first and the original checklist string second. The comprehension unpacks those positions as number and text. start=7 changes the counter’s first value; it does not skip the first seven input items. All three source items remain in the result.

Reversing the input makes Store sample receive 7, illustrating why the display counter should not replace a durable record ID. Empty input produces no pairs; start does not manufacture an item. Materializing pairs as a list is useful for inspection here, but a normal for loop can consume enumerate directly without creating that intermediate list.

Avoid these mistakes

Do not use the displayed number as a zero-based list index when start is nonzero. Keep any actual business identifier inside the item itself. If you filter a checklist, decide whether numbering should happen before filtering to preserve source positions or afterward to create consecutive visible numbers.