enumerate — when AI needs the index too

About half the loops Cursor writes need both the value and its position. The third item. Line 12 of the file. Step 4 of the workflow. You can't get the position from a plain for x in items loop — that just hands you values, with no way to tell which one is which.

The wrong way to fix it (which non-coders try first, and which AI sometimes mimics):

for i in range(len(names)):
    name = names[i]
    print(i, name)

That's a four-line C-flavored solution to a one-line Python problem. Python ships a built-in for exactly this case.

The right shape: enumerate

for i, value in enumerate(items):
    ...

enumerate walks any sequence and yields (index, value) tuples. The for i, value in ... line unpacks each tuple into two named variables — i for the position, value for the item.

Read it as: "for each (index, name) pair when you walk the list…"

By default, the index starts at 0. If you want it to start at 1 (common for human-readable output like "step 1, step 2, step 3"), pass start=1:

for i, name in enumerate(names, start=1):
    print(f"{i}. {name}")

That's the entire feature. One built-in, two arguments at most.

A worked example

The editor on the right has three names:

names = ["maya", "marcus", "riley"]

for i, name in enumerate(names):
    print(i, name)

Each iteration, enumerate produces a tuple — first (0, "maya"), then (1, "marcus"), then (2, "riley"). The for i, name syntax splits each tuple in half: i gets the number, name gets the string.

Output:

0 maya
1 marcus
2 riley

Same logic as the four-line range(len(...)) version, with a third of the code and zero off-by-one risk.

Where AI specifically gets indexing wrong

When you read AI code that walks a list with explicit indexes, watch for these patterns:

1. for i in range(len(items)): followed by items[i]. This is the C-style version. It works, but it's the long way and it exposes the off-by-one bugs we covered earlier. Cursor sometimes writes it when it should write enumerate. When you see this shape, mentally rewrite it to for i, item in enumerate(items): and read from there.

2. Tracking the index manually with a counter.

   i = 0
   for item in items:
       print(i, item)
       i += 1
   

   Same anti-pattern, two extra lines. Pure enumerate replacement.

3. Starting the count at the wrong place. Some AI-generated "human-readable" output starts at 0 when it should start at 1 ("Step 0: …" looks weird). The fix is enumerate(items, start=1), not a manual i + 1 inside the f-string.

Run the editor. Three names, indexed 0, 1, 2. No range(len(...)) needed.