Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Programming > Python > Re: Double sided double underscored variable names

Reply
Thread Tools

Re: Double sided double underscored variable names

 
 
Chris Angelico
Guest
Posts: n/a
 
      09-11-2012
On Wed, Sep 12, 2012 at 8:48 AM, Joshua Landau
<(E-Mail Removed)> wrote:
> Well, the problem is that a lot of collisions aren't predictable.
> "locals()['foo'] = 2", for example. If it weren't for Python's annoying
> flexibility* I would definitely do something very close to what you suggest.
> Remember that "locals()" isn't Python's only introspection tool. How about
> "from foo import *"?


You're not supposed to mutate locals(), but I suppose globals() works
the same way.

Inline functions? I like this idea. I tend to want them in pretty much
any language I write in.

ChrisA
 
Reply With Quote
 
 
 
 
Steven D'Aprano
Guest
Posts: n/a
 
      09-12-2012
And again, Joshua's original post is not available from my provider.
Joshua, I suspect that something about your post is being seen as spam
and dropped by at least some providers.


On Wed, 12 Sep 2012 08:52:10 +1000, Chris Angelico wrote:

> On Wed, Sep 12, 2012 at 8:48 AM, Joshua Landau
> <(E-Mail Removed)> wrote:
>>
>> Well, the problem is that a lot of collisions aren't predictable.
>> "locals()['foo'] = 2", for example. If it weren't for Python's annoying
>> flexibility*


I can't see your footnote there, so you may have already covered this,
but for the record, what you call Python's "annoying flexibility" is
fundamental to Python's programming model and done so for good reasons.
The ability to shadow built-ins is, at times, incredibly useful rather
than annoying.

The world is full of bondage and domination languages that strongly
restrict what you can do. Python doesn't need to be another one of them.
Python's optimizing compiler, PyPy, is able to optimize code very well
without such restrictions.


>> I would definitely do something very close to what you
>> suggest. Remember that "locals()" isn't Python's only introspection
>> tool. How about "from foo import *"?


I wouldn't call "import *" an introspection tool. At least, no more so
than print.


> You're not supposed to mutate locals(),


It's not so much you're not allowed to do it, but that the result of
making changes to locals() inside a function is implementation dependent:

CPython 2: writing to the dict returned by locals() will work, but the
changes will not be reflected in the actual local variables, except under
very restricted circumstances;

CPython 3: those restricted circumstances that allowed writes to locals()
to modify local variables are now SyntaxErrors;

Stackless: presumably the exact same behaviour as CPython (since
Stackless is a fork, not a re-implementation);

Jython: the same as CPython;

IronPython: writes to locals() will modify the corresponding local
variable.


Outside of a function, locals() returns globals() and writes will always
modify the global variable (this is a language guarantee).

> but I suppose globals() works the same way.
>
> Inline functions? I like this idea. I tend to want them in pretty much
> any language I write in.


What do you mean by in-line functions? If you mean what you literally
say, I would answer that Python has that with lambda.

But I guess you probably mean something more like macros.


--
Steven
 
Reply With Quote
 
 
 
 
Chris Angelico
Guest
Posts: n/a
 
      09-12-2012
On Wed, Sep 12, 2012 at 11:38 AM, Joshua Landau
<(E-Mail Removed)> wrote:
> On 12 September 2012 02:14, Steven D'Aprano
> <(E-Mail Removed)> wrote:
>>
>> And again, Joshua's original post is not available from my provider.
>> Joshua, I suspect that something about your post is being seen as spam
>> and dropped by at least some providers.

>
> I am sorry to ask this, but in the meantime can someone who isn't
> spam-filtered repost my messages? I'll give them a cookie!
> To repeat my previous post, I'm using GMail and posting to
> http://www.velocityreviews.com/forums/(E-Mail Removed). If that is what I'm meant to be doing, I'll try
> another email address.


Mailing to python-list@python from Gmail is exactly what I do, and far
as I know, none of my posts are getting lost. But then, I'm seeing all
your posts, too, so maybe I just don't know when my posts don't go
through.

>> On Wed, 12 Sep 2012 08:52:10 +1000, Chris Angelico wrote:
>>
>> > Inline functions? I like this idea. I tend to want them in pretty much
>> > any language I write in.

>>
>> What do you mean by in-line functions? If you mean what you literally
>> say, I would answer that Python has that with lambda.
>>
>> But I guess you probably mean something more like macros.

>
> No, just multi-line lambda. Macros, if my knowledge of lower-level languages
> is valid, would be sorta' silly in Python.


Ah, okay. I was thinking more along the lines of what you call macros,
but in the C++ sense of inline functions. In C, macros are handled at
precompilation stage, and are dangerous. Classic example:

#define squared(x) x*x

x_squared = squared(6+7)

So your macros end up littered with parentheses, and it still doesn't
solve anything, as the argument still gets evaluated twice. (A problem
if it has side effects - eg if it's a function call.)

What I'm thinking of, though, is like C++ functions. You can put the
'inline' keyword onto any function, and the compiler will do its best
to inline it (in fact, a good optimizing compiler will inline things
regardless, but that's a separate point). I can write:

inline int squared(int x) {return x*x;}

and C++ will add no function overhead, but will still do all the
proper evaluation order etc.

Of course, C++ doesn't allow monkeypatching, so you'll never have
semantic differences from inlining. It's just a performance question.
But I use inline functions like constants - for instance, I could
create a function that converts a database ID into an internal
reference number, and I can change the definition of that function in
one place and have it apply everywhere, just like if I wanted to
change the definition of math.PI to 3.142857 for fun one day. Of
course I can use a normal (out-of-line) function for this, but that
has overhead in most languages. Hence, wanting inline functions.

ChrisA
 
Reply With Quote
 
Joshua Landau
Guest
Posts: n/a
 
      09-12-2012
On 12/09/2012, Chris Angelico <(E-Mail Removed)> wrote:
> On Wed, Sep 12, 2012 at 11:38 AM, Joshua Landau
> <(E-Mail Removed)> wrote:
>> On 12 September 2012 02:14, Steven D'Aprano
>> <(E-Mail Removed)> wrote:
>>>
>>> On Wed, 12 Sep 2012 08:52:10 +1000, Chris Angelico wrote:
>>>
>>> > Inline functions? I like this idea. I tend to want them in pretty much
>>> > any language I write in.
>>>
>>> What do you mean by in-line functions? If you mean what you literally
>>> say, I would answer that Python has that with lambda.
>>>
>>> But I guess you probably mean something more like macros.

>>
>> No, just multi-line lambda. Macros, if my knowledge of lower-level
>> languages
>> is valid, would be sorta' silly in Python.

>
> Ah, okay. I was thinking more along the lines of what you call macros,
> but in the C++ sense of inline functions. In C, macros are handled at
> precompilation stage, and are dangerous. Classic example:
>
> #define squared(x) x*x
>
> x_squared = squared(6+7)
>
> So your macros end up littered with parentheses, and it still doesn't
> solve anything, as the argument still gets evaluated twice. (A problem
> if it has side effects - eg if it's a function call.)
>
> What I'm thinking of, though, is like C++ functions. You can put the
> 'inline' keyword onto any function, and the compiler will do its best
> to inline it (in fact, a good optimizing compiler will inline things
> regardless, but that's a separate point). I can write:
>
> inline int squared(int x) {return x*x;}
>
> and C++ will add no function overhead, but will still do all the
> proper evaluation order etc.
>
> Of course, C++ doesn't allow monkeypatching, so you'll never have
> semantic differences from inlining. It's just a performance question.
> But I use inline functions like constants - for instance, I could
> create a function that converts a database ID into an internal
> reference number, and I can change the definition of that function in
> one place and have it apply everywhere, just like if I wanted to
> change the definition of math.PI to 3.142857 for fun one day. Of
> course I can use a normal (out-of-line) function for this, but that
> has overhead in most languages. Hence, wanting inline functions.


Interesting. I'd overestimated macros and underestimated inline functions.

I am not sure how to make a version of that with scope-compatibility. Inlining
inline_def f(y): x = y +1
would hopefully not change the outside scope*, but I'm not sure how to
make that.

I could make it work by banning "=", but then it's almost a macro but with
internal_a = input_a
internal_b = input_b
....
at the start...

* If I understand rightly
 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Re: Double sided double underscored variable names Chris Angelico Python 1 09-12-2012 12:51 AM
ASPX, VBScript, JavaScript, Double-Underscored Variables and setTimeOut Shadow Lynx ASP .Net 10 08-09-2006 07:40 PM
Should I be concerned about buying DVD18s (Double-sided, double-layered) The Man With No Name DVD Video 3 02-04-2006 01:45 AM
Double-Sided freesoft_2000 Java 1 02-01-2005 10:11 AM
double-sided ram strand Computer Support 9 04-10-2004 02:09 AM



Advertisments