You're right. Invalid signature is TypeError.

```
In [1]: def p(a, b):
   ...:     return a+b
   ...:

In [2]: p(1)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-febfdd3449e6> in <module>()
----> 1 p(1)

TypeError: p() takes exactly 2 arguments (1 given)
```