Hi,

Here's something I wanted in Python for many years. If this has been discussed in the past, please refer me to that discussion.

On one hand, it's something that I can't imagine the python-dev community supporting. On the other hand, it would maintain backward compatibility.

I wish there were a 100 more built-in exceptions in Python, that will be very specific about what went wrong.

If I do this: 

    >>> x, y = range(3)

I know it'll raise a ValueError, because I've memorized that, but it did take me a few years to remember where I should expect ValueError and where I should expect TypeError.

It would be nice if the operation above raised UnpackingOverflowError, which will be a subclass of UnpackingError, along with UnpackingUnderflowError.  UnpackingError can be a subclass of ValueError, for backward compatibility.

Similarly, if I did this: 

    >>> def f(x, y): return x + y
    >>> f(1)

I would get a TypeError. Would be a lot cooler if I got MissingArgumentsError, which would be a subclass of SignatureError, which would be a subclass of TypeError.

There are 2 reasons I want this: 

1. When I'm writing a try..except clause, I want to catch a specific exception like MissingArgumentsError rather than ValueError or TypeError. They're too ubiquitous. I don't want some other unexpected failure producing the same ValueError and triggering my except clause. 

2. When I get an error, especially from some shitty corporate system that truncates the traceback, I want to get as many hints as possible about what went wrong.

It's true that today, most Python exceptions have good text in their message, like "TypeError: f() missing 1 required positional argument: 'y'". But that isn't guaranteed everywhere, and specific exception types could help.

What do you think? 

Ram.