The `+` is not necessary here, just use implicit string continuation:
```
    warnings.warn("Normalization factor of kernel is "
                              "exceptionally large > 100.")
```

Also considering that `100` is a magic number, and wholly arbitrary at that, it should at least be a module-level "constant" that can be tweaked:

```
MAX_NORMALIZATION = 100
```

or something.  Use it in both the comparison and in formatting the warning message.