I think Serhiy's response is excellent and agree with it. My gut reaction is "this looks like Perl" (and not in a good way), but more specifically it makes the control flow almost invisible. So I'm definitely -1 on this.

The current while True ... break idiom is not pretty, but it's also very clear and obvious, and the control flow is immediately visible.

One thing I do like about the proposal is the bare "while:", and I think that syntax is obvious and might be worth keeping (separately to the rest of the proposal). A bare "while:" (meaning "while True:") seems somehow less insulting to the intelligence, is still clear, and has precedent in Go's bare "for { ... }".


On Wed, Sep 6, 2017 at 2:42 AM, Serhiy Storchaka <storchaka@gmail.com> wrote:
06.09.17 03:11, R. David Murray пише:
I've written a PEP proposing a small enhancement to the Python loop
control statements.  Short version: here's what feels to me like a
Pythonic way to spell "repeat until":

         <do stuff>
         break if <done condition>

The PEP goes into some detail on why this feels like a readability
improvement in the more general case, with examples taken from
the standard library:


Unlike Larry, I don't have a prototype, and in fact if this idea
meets with approval I'll be looking for a volunteer to do the actual


PS: this came to me in a dream on Sunday night, and the more I explored
the idea the better I liked it.  I have no idea what I was dreaming about
that resulted in this being the thing left in my mind when I woke up :)

This looks rather like Perl way than Python way.

"There should be one-- and preferably only one --obvious way to do it."

This proposing saves just a one line of the code. But it makes "break" and "continue" statement less visually distinguishable as it is seen in your example from uuid.py.

If allow "break if" and "continue if", why not allow "return if"? Or arbitrary statement before "if"? This adds PHP-like inconsistency in the language.

Current idiom is easier for modification. If you add the second condition, it may be that you need to execute different code before "break".

    while True:
        <do stuff>
        if not <condition>:
            <exit code>
        <do stuff 2>
        if not <condition >:
            <exit code 2>

It is easy to modify the code with the current syntax, but the code with the proposed syntax should be totally rewritten.

Your example from sre_parse.py demonstrates this. Please note that pre-exit code is slightly different. In the first case self.error() is called with one argument, and in the second case it is called with two arguments. Your rewritten code is not equivalent to the existing one.

Other concern is that the current code is highly optimized for common cases. Your rewritten code checks the condition "c is None" two times in common case.

I'm -1 for this proposition.