PEP-315 ("do" loop)

Josiah Carlson jcarlson at
Wed Feb 18 20:11:11 CET 2004

> 1. It's clever, addresses a definite "wart",  and is syntactically 
> similar to try/except. But it's syntax seems like an acquired taste to me.

Clever, perhaps.  Ugly and confusing, yes.  Solves a 'problem' that 
isn't a problem, most definitely.

> while 1:
>     line = sys.stdin.readline()
>     if line == "\n":
>         break

I use these all the time, and find them conceptually convenient.  Most 
Junior/Senior undergraduate computer science majors have no problems 
understanding this concept, so I don't think it is necessary to change 
the while syntax.

> until line == "\n":
>     line = sys.stdin.readline()
> Would be defined to work exactly like a while loop except the test is 
> not evaluated the first time through the loop. Wouldn't this be akin to 
> checking at the end of the loop, while maintaining a more while-ish syntax?

As others have said, it is not obvious that until implies "don't test 
the condition the first time through".

> Is this at all useful or is something of the order of PEP-315 the way to 
> go?

Personally, I find altering the syntax of while, or adding the 'do' to 
be a wart.  I've never had problems understanding or writing code like 
the following;
while 1:
     if <condition>:  break

If I had a vote, I'd be -1 on PEP 315.

  - Josiah

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