For Loop
A loop that iterates over each item of an iterable.
- Iterates by item, not by index.
- Use enumerate for (index, value), zip for parallel iteration.
- range(n) gives 0..n-1.
When to use: Training loops, evaluation passes, almost every script.
Example: for epoch in range(10): train_one_epoch(model). for i, batch in enumerate(loader): ...