PEP 315: Enhanced While Loop

[W Isaac Carroll]

Here are my responses to the ideas discussed since I posted PEP 315.

* PEP was submitted to be rejected

If the Python community rejects the PEP so be it, but I really would 
like a statement that works like this.

* "Python ain't broken. Please don't fix it."

Python is not broken. But if Python could not be improved we wouldn't 
need PEPs at all.

* "do" is unclear
* do-while in other languages doesn't have 2nd suite
* do-while-while ambiguity
* unseen "do" changes the meaning of seen "while"

These are problems which I had not considered when writing the PEP. It 
seems to me that the best way to solve them is to choose different 
keywords. How about:

     perform:
         <setup code>
     whilst <condition>:
         <loop body>

:)

* indentation should indicate execution path
* it's not clear that both blocks execute each iteration

These are good points. There is no precedent in Python for two 
indentation groups which are conceptually the same block. Indenting the 
while statement to the same level as the rest of the block would solve 
this problem but it would hide the loop condition. I prefer the pattern 
recommended in the PEP because it clearly indicates the loop condition, 
but I do not know for certain that it is better (clearer, more pythonic, 
etc).

* a post-test loop is sufficient

The problem I presented in the PEP could not be solved with a post-test 
loop. However, please note that a post-test loop could easily be 
constructed using the do-while syntax of the PEP.

* infinite loop with break is a well-known idiom in other languages and
   is a good way of expressing this behavior

Experienced programmers are used to writing infinite loops and breaking 
out of them. However, saying "while True" does not clearly express the 
purpose and behavior of the loop. Just because it's traditional to write 
infinite loops does not mean that it's a good way to program.

I feel that the use of break is similar to the use of goto in the past. 
Goto was necessary because of the limited control structures available 
in early languages, but as for, while, if-else, functions, and other 
powerful control structures came into use, the goto was no longer 
necessary and gradually disappeared. If we adopt loop constructs of 
sufficient power and flexibility, the break statement will also no 
longer be needed, and will disappear from use.

In other words, if all you have is an infinite loop, everything looks 
like it needs one.

If I have not adequately responded to your comment, please re-post it or 
send me email.

TTFN