[Python-ideas] Documenting Python warts on Stack Overflow

[Chris Angelico]

On Wed, Jan 2, 2013 at 10:17 AM, alex23 <wuwei23 at gmail.com> wrote:
> On Jan 2, 8:16 am, Chris Angelico <ros... at gmail.com> wrote:
>> It's a little odd what you can and can't do,
>> until you understand the underlying system fairly well. It's something
>> that's highly unlikely to change; one of the premises would have to be
>> sacrificed (or at least modified) to achieve it.
>
> By this definition, though, every feature of Python that someone
> doesn't understand is a wart. For a new user, mutable default
> parameters is a wart, but once you understand Python's execution &
> object models, it's just the way the language is.
>
> Generally, I find "wart" means "something the user doesn't like about
> the language even if it makes internal sense".

That's pretty much it, yeah. The warts of Python are the gotchas that
need to be grokked before you can call yourself fluent in the
language. Might feel as though the designers "got it wrong", or were
making an arbitrary choice, but whatever it is, the language behaves
that way and you have to get to know it. I agree that mutable defaults
as a wart.

PHP's scoping rules are simpler than Python's. A variable inside a
function is local unless it's explicitly declared global; function
names are global. (That's not the whole set of rules, but close enough
for this argument.) Python, on the other hand, adds the oddity that a
name referenced inside a function is global unless, somewhere in that
function, it's assigned to. This is a Python wart that bites people
(see the first question in http://toykeeper.net/warts/python/ for
instance), but it's a consequence of putting "variables" and
"functions" into a single namespace called "name bindings", plus the
decision to not require variable declarations (C, for instance, has
the same notion of "everything's a name", but instead of declaring
globals, declares locals). Python's scoping rules are vastly superior
to PHP's, but a bit more complicated, and may need a bit of
explanation.

(Incidentally, of all the warts listed in the page I linked above, two
give a quick and easy error message, two have better ways of doing
things (don't use +=, use append/extend), and only one is really a
wart - mutable default values. Well, that and the behaviour of += on
something in a tuple, but .extend dodges that one too.)

Documenting these sorts of oddities is a good thing, as long as the
underlying goal is one of new programmer education and not "hey you
idiots who develop this language, here's all the things you did
wrong".

ChrisA