PEP 548: More Flexible Loop Control
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":
while: <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:
https://www.python.org/dev/peps/pep-0548/
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 implementation.
--David
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 :)
On Wed, Sep 6, 2017 at 10:11 AM, R. David Murray rdmurray@bitdance.com wrote:
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":
while: <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:
https://www.python.org/dev/peps/pep-0548/
Is "break if" legal in loops that have their own conditions as well, or only in a bare "while:" loop? For instance, is this valid?
while not found_the_thing_we_want: data = sock.read() break if not data process(data)
Or this, which uses the condition purely as a descriptor:
while "moar socket data": data = sock.read() break if not data process(data)
Also - shouldn't this be being discussed first on python-ideas?
ChrisA
On Wed, 06 Sep 2017 15:05:51 +1000, Chris Angelico rosuav@gmail.com wrote:
On Wed, Sep 6, 2017 at 10:11 AM, R. David Murray rdmurray@bitdance.com wrote:
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":
while: <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:
https://www.python.org/dev/peps/pep-0548/Is "break if" legal in loops that have their own conditions as well, or only in a bare "while:" loop? For instance, is this valid?
while not found_the_thing_we_want: data = sock.read() break if not data process(data)
Yes.
Or this, which uses the condition purely as a descriptor:
while "moar socket data": data = sock.read() break if not data process(data)
Yes.
Also - shouldn't this be being discussed first on python-ideas?
Yep, you are absolutely right. Someone has told me I also missed a related discussion on python-ideas in my searching for prior discussions. (I haven't looked for it yet...)
I'll blame jet lag :)
--David
I'm actually not in favor of this. It's another way to do the same thing. Sorry to rain on your dream!
On Wed, Sep 6, 2017 at 9:34 AM, R. David Murray rdmurray@bitdance.com wrote:
On Wed, 06 Sep 2017 15:05:51 +1000, Chris Angelico rosuav@gmail.com wrote:
On Wed, Sep 6, 2017 at 10:11 AM, R. David Murray rdmurray@bitdance.com
wrote:
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":
while: <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:
https://www.python.org/dev/peps/pep-0548/Is "break if" legal in loops that have their own conditions as well, or only in a bare "while:" loop? For instance, is this valid?
while not found_the_thing_we_want: data = sock.read() break if not data process(data)
Yes.
Or this, which uses the condition purely as a descriptor:
while "moar socket data": data = sock.read() break if not data process(data)
Yes.
Also - shouldn't this be being discussed first on python-ideas?
Yep, you are absolutely right. Someone has told me I also missed a related discussion on python-ideas in my searching for prior discussions. (I haven't looked for it yet...)
I'll blame jet lag :)
--David _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/ guido%40python.org
On Wed, 06 Sep 2017 09:43:53 -0700, Guido van Rossum guido@python.org wrote:
I'm actually not in favor of this. It's another way to do the same thing. Sorry to rain on your dream!
So it goes :) I learned things by going through the process, so it wasn't wasted time for me even if (or because) I made several mistakes. Sorry for wasting anyone else's time :(
--David
No worries. We all learned stuff!
On Wed, Sep 6, 2017 at 4:22 PM, R. David Murray rdmurray@bitdance.com wrote:
On Wed, 06 Sep 2017 09:43:53 -0700, Guido van Rossum guido@python.org wrote:
I'm actually not in favor of this. It's another way to do the same thing. Sorry to rain on your dream!
So it goes :) I learned things by going through the process, so it wasn't wasted time for me even if (or because) I made several mistakes. Sorry for wasting anyone else's time :(
--David _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/ guido%40python.org
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":
while: <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:
https://www.python.org/dev/peps/pep-0548/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 implementation.
--David
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> break <do stuff 2> if not <condition >: <exit code 2> break
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.
On 6 September 2017 at 08:42, 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":
while: <do stuff> break if <done condition>I'm -1 for this proposition.
I also think this is not worth it. This will save few lines of code but introduces some ambiguity and makes syntax more complex.
-- Ivan
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 { ... }".
-Ben
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":
while: <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:
https://www.python.org/dev/peps/pep-0548/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 implementation.
--David
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> break <do stuff 2> if not <condition >: <exit code 2> breakIt 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.
Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/benhoyt% 40gmail.com
https://www.youtube.com/watch?v=pNe1wWeaHOU&list=PLYI8318YYdkCsZ7dsYV01n... Thank you, -Alex Goretoy
On Wed, Sep 6, 2017 at 7:05 PM, Ben Hoyt benhoyt@gmail.com wrote:
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 { ... }".
-Ben
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":
while: <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:
https://www.python.org/dev/peps/pep-0548/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 implementation.
--David
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> break <do stuff 2> if not <condition >: <exit code 2> breakIt 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.
Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/benhoyt%40gmail.com
Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/agoretoy%40gmail.com
participants (7)
-
alex goretoy -
Ben Hoyt -
Chris Angelico -
Guido van Rossum -
Ivan Levkivskyi -
R. David Murray -
Serhiy Storchaka