`inspect` doesn't work on built-in Python functions, because they are just compiled directly in C.  E.g., this code would fail:

```python
nengo.Node(output=math.sin)
```

I spent a while working on this before, but couldn't find any good way to inspect those functions.  I believe all I ended up doing was trying to call them with 0 arguments, catching the exception, trying to call them with 1 argument, catching the exception, etc.