Use `np.float32()` instead.
### What problem does this PR solve?
Using `eval()` can lead to code injections.
I think `eval()` is only used to parse a floating point number here.
This change preserves the correct behavior if the string `"None"` is
supplied. But if that behavior isn't intended then this part could be
just deleted instead, since `np.float32()` is parsing strings anyway:
```Python
if isinstance(scale, str):
scale = eval(scale)
```
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
6b389e01b5