What happens when I omit the brackets when trying to catch multiple exceptions?

Question

I just tried writing this:

try:
    # do something
except ValueError, IndexError:
    # do something else

And then got very confused when my program still threw an IndexError because I thought I was catching it.

If it doesn't catch the IndexError, what exactly does this code do? It doesn't seem to be a syntax error.

Answer 1

Because this mistake/problem is so common, the syntax changes for Python3. You code would be equivalent to

try:
    # do something
except (ValueError, ) as IndexError:
    # do something else

You would have seen that this is obviously wrong.

The new syntax works back as far as Python2.6

This works ok

try:
    # do something
except (ValueError, IndexError):
    # do something else

but often you want to do something with the exception, so you can write

try:
    # do something
except (ValueError, IndexError) as e:
    # do something with e

Answer 2

It catches ValueErrors, and assigns the caught exception to the name IndexError. You want this:

except (ValueError, IndexError):