This caught a couple of cases of us doing:
```python
for i in range(len(x)):
v = x[i]
```
which are places to use enumerate instead.
It also caught a couple of cases of:
```python
assert len(x) == len(y)
for i in range(len(x)):
xv = x[i]
yv = y[i]
```
Which should instead be using zip()
```python
for xv, yv in zip(x, y):
...
```