ValueError vs IndexError, unpacking arguments with string.split

[Dan Sommers]

On 11/30/18 10:57 AM, Morten W. Petersen wrote:
 > On Fri, Nov 30, 2018 at 4:25 PM Dan Sommers 
<2QdxY4RzWzUUiLuE at potatochowder.com> wrote:

 >> Python validates that the right hand side contains exactly the right
 >> number of elements before beginning to unpack, presumably to ensure a
 >> successful operation before failing part way through.

 > Hm.  Well I like the simplicity and abstraction of Python, it makes it
 > a very productive language.

Agreed, and hold that thought.

 > But since you mention it, why is it necessary to ensure a successful
 > operation?
 >
 > Is it so that when
 >
 > a,b,c = [1,2]
 >
 > fails, none of the variables a,b,c have been assigned to, and because
 > of that, one avoids "rolling back" any assignment that would have been
 > done without checking the right-hand argument first ?

That's what I was getting at, but apparently failed to express clearly.

Yes, there are use cases for a short iterator just not assigning the
rest of the variables, and for a long iterator using only what it needs,
but also explicit is better than implicit, and errors should never pass
silently, and other bits of wisdom learned from horrible debugging
experiences.