[Python-ideas] Retrying EAFP without DRY

[Ron Adam]

On Fri, 2012-01-20 at 16:36 -0800, Mike Meyer wrote:
> The behavior change from except is that instead of exiting the "try"
> statement when the "retry" clause ends, it restarts the try
> clause. In python, this code:
> 
>     try:
>         # try block
>     except:
>         # except block
>     retry:
>         # retry block
>     else:
>         # else block
>     finally:
>         # finally block
> 
> Would provide the same behavior as this code:
> 
>     while True:
>         try:
>             # try block
>         except:
>             # except block
>         retry:
>             # retry block
>         else:
>             # else block
>         finally:
>             # finally block
>             break

This looks like it would be very tricky to get right from a python
programming stand point.  Remember that python is full of one time
iterators that won't repeat properly on a second try. Also many function
calls mutate the arguments.  So it's possible that a data structure
could be changed on the first try, and give different results on a
second try in an unexpected way.

Cheers,
   Ron