[Python-Dev] Update PEP 7 to require curly braces in C (original) (raw)

Brett Cannon brett at python.org
Tue Jan 19 12:07:36 EST 2016

On Tue, 19 Jan 2016 at 00:48 M.-A. Lemburg <mal at egenix.com> wrote:

On 19.01.2016 00:20, Brett Cannon wrote: > On Sun, 17 Jan 2016 at 11:10 Brett Cannon <brett at python.org> wrote: > >> While doing a review of http://bugs.python.org/review/26129/ I asked to >> have curly braces put around all if statement bodies. Serhiy pointed out >> that PEP 7 says curly braces are optional: >> https://www.python.org/dev/peps/pep-0007/#id5. I would like to change >> that. >> >> My argument is to require them to prevent bugs like the one Apple made >> with OpenSSL about two years ago: >> https://www.imperialviolet.org/2014/02/22/applebug.html. Skipping the >> curly braces is purely an aesthetic thing while leaving them out can lead >> to actual bugs. >> >> Anyone object if I update PEP 7 to remove the optionality of curly braces >> in PEP 7? >> > > Currently this thread stands at:

Make that: > +1 > Brett > Ethan > Robert > Georg > Nick > Maciej Szulik > +0 > Guido > -0 > Serhiy > -1 MAL > Victor (maybe; didn't specifically vote) > Larry > Stefan There are plenty other cases where typos can ruin the flow of your code in C; the discussed case is not a very common one. I find the whole discussion a bit strange: In Python we're advocating not having to use curly braces, because whitespace already provides the needed semantics for us, yet you are now advocating that without adding extra curly braces we'd be in danger of writing wrong code.

Yes, because in one language whitespace represents semantics while the other is just formatting; I don't have to question the meaning of when something is indented in Python, but in C I have to question whether the indentation is an accident or the missing braces is the accident.

The Apple bug can happen in Python just as well: if a: runiftrue() else: runiffalse() can turn into (say by hitting a wrong key in the editor): if a: runiftrue() runiffalse() (runiffalse is now run when a is true, and nothing is done in case a is false) So what's the correct way to address this ? It's having a test for both branches (a is true, a is false), not starting to write e.g. if a: runiftrue() if not a: runif false() to feel more "secure".

OK, but what if the block was instead:

if (a) run_if_true(); Py_INCREF(a);

? Unit tests are not going to easily turn up a refcount leak, and the number of times I have needed to email python-dev when Antoine's daily refcount email has found a leak for several days shows people do not watch closely for this. It's one thing when the expressions are obviously mutually exclusive, but that's an ideal case. This isn't always about losing an else statement as it can come from inserting a new statement and not noticing that the braces are missing.

Also note that the extra braces won't necessarily help you. If you remove "else" from: if (a) { runiftrue(); } else { runiffalse(); } you get exactly the same Apply bug as before, only with more curly braces. This all sounds a bit like security theater to me ;-)

That's fine. I also want format consistency by always using braces.

I'd say: people who feel better using the extra braces can use them, while others who don't need them can go ahead as always ... and both groups should write more tests :-)

Well, I'm dropping out of this discussion because I have enough on my plate with the GitHub migration than to keep fighting this.

BTW: There are other things in PEP 7 which should probably be updated instead, e.g. it still says we should use C89, but we're having more and more C99 code (mostly new library functions) in CPython.

That's a whole other discussion (which I support, but I'm not going to lead since I'm burned out at the moment on C-related discussions).

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