Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #36202

Re: pygame - importing GL - very bad...

From someone <newsboost@gmail.com>
Newsgroups comp.lang.python
Subject Re: pygame - importing GL - very bad...
Date 2013-01-05 20:49 +0100
Organization A noiseless patient Spider
Message-ID <kca03g$olj$1@dont-email.me> (permalink)
References (7 earlier) <mailman.104.1357349785.2939.python-list@python.org> <kc90g4$p5d$1@dont-email.me> <mailman.111.1357386440.2939.python-list@python.org> <kc98gm$21c$1@dont-email.me> <mailman.115.1357392442.2939.python-list@python.org>

Show all headers | View raw

On 01/05/2013 02:27 PM, Chris Angelico wrote:
> On Sun, Jan 6, 2013 at 12:06 AM, someone <newsboost@gmail.com> wrote:

>> In any case I think we understand each other.
>
> That's one of the links I just posted :) It's not just a naming
> difference, though. With Pascal's pass-by-reference semantics, this
> code would act differently:
>
> def foo(x):
>    x = 5
>
> a = 2
> foo(a)
> print(a)
>
> Python prints 2, because the assignment to x just rebinds the name
> inside foo. True pass-by-reference actually changes the caller's
> variable. C can achieve this by means of pointers; in Python, you can

I thought that python also used "true" pass-by-reference, although I 
haven't figured out exactly when I have this problem. I can just see 
that sometimes I get this problem and then I need to copy the variable, 
if I don't want the original data of the variable to be overwritten...

> pass and mutate a list, thus:
>
> def foo(x):
>    x[0] = 5 # Dereference the pointer, kinda
>
> x=[None] # Declare a pointer variable, ish
> x[0] = 2
> foo(x) # Don't forget to drop the [0] when passing the pointer to
> another function
> print(x[0]) # Prints 5. See? We have pass-by-reference!

Yes, something like this has happened to me in my python code... Not 
sure if my example was exactly like this, but I remember something where 
I found this to be a problem that I had to fix.

> But otherwise, rebinding names in the function has no effect on
> anything outside. Among other things, this guarantees that, in any

hmm. ok.... So it's not true pass-by-reference like I thought... That's 
interesting.

> situation, a name referencing an object can be perfectly substituted
> for any other name referencing the same object, or any other way of
> accessing the object.
>
> def foo(lst):
>    lst[0]=len(lst)
>
> x = [10,20,30]
> y = x
> foo(x) # These two...
> foo(y) # ... are identical!

This is something I've experienced from my own coding, I think...

> This is a philosophy that extends through the rest of the language. A
> function returning a list can be directly dereferenced, as can a list
> literal:
>
> def foo():
>    return [0,1,4,9,16]
>
> print( ["Hello","world!","Testing","Testing","One","Two","Three"][foo()[2]] )

That prints out "One"... I think I understand - that's interesting too...

> This is a flexibility and power that just doesn't exist in many older
> languages (C and PHP, I'm looking at you). Object semantics make more
> sense than any other system for a modern high level language, which is
> why many of them do things that way.

I agree, that I think python is really great and it's fast to do 
something useful. Not sure I still understand exactly all aspects of 
this pass-by-value and by-references, but in any case I know enough to 
watch out for this problem and once I see I have a problem, I can also 
take care of it and solve it by making a copy. I think maybe after 3-6-9 
months more of working with python, I should be fully confident with 
this. Thanks for taking the time to explain a bit of this to me...

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-01 12:00 +0100
  Re: pygame - importing GL - very bad... Chris Angelico <rosuav@gmail.com> - 2013-01-01 22:13 +1100
    Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-02 00:49 +0100
      Re: pygame - importing GL - very bad... Michael Torrie <torriem@gmail.com> - 2013-01-02 14:57 -0700
        Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-03 02:53 +0100
          Re: pygame - importing GL - very bad... "Mike C. Fletcher" <mcfletch@vrplumber.com> - 2013-01-03 09:09 -0500
            Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-05 02:10 +0100
              Re: pygame - importing GL - very bad... Dave Angel <d@davea.name> - 2013-01-04 20:30 -0500
                Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-05 11:49 +0100
                Re: pygame - importing GL - very bad... Dave Angel <d@davea.name> - 2013-01-05 06:23 -0500
                Re: pygame - importing GL - very bad... Chris Angelico <rosuav@gmail.com> - 2013-01-05 22:47 +1100
                Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-05 14:06 +0100
                Re: pygame - importing GL - very bad... Chris Angelico <rosuav@gmail.com> - 2013-01-06 00:27 +1100
                Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-05 20:49 +0100
                Re: pygame - importing GL - very bad... alex23 <wuwei23@gmail.com> - 2013-01-06 03:37 -0800
                Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-06 13:46 +0100
      Re: pygame - importing GL - very bad... Andrew Berg <bahamutzero8825@gmail.com> - 2013-01-02 16:30 -0600
        Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-03 03:02 +0100
  Re: pygame - importing GL - very bad... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-01-01 11:49 +0000
    Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-02 00:49 +0100
      Re: pygame - importing GL - very bad... Nobody <nobody@nowhere.com> - 2013-01-02 03:01 +0000
        Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-02 04:43 +0100
        Re: pygame - importing GL - very bad... alex23 <wuwei23@gmail.com> - 2013-01-02 01:52 -0800
          Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-02 15:04 +0100
      Re: pygame - importing GL - very bad... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-01-02 07:39 +0000
        Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-02 15:06 +0100
  Re: pygame - importing GL - very bad... Peter Otten <__peter__@web.de> - 2013-01-01 13:56 +0100
    Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-02 00:50 +0100
      pylint, was Re: pygame - importing GL - very bad... Peter Otten <__peter__@web.de> - 2013-01-02 13:07 +0100
        Re: pylint, was Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-02 15:09 +0100
          Re: pylint, was Re: pygame - importing GL - very bad... Dave Angel <d@davea.name> - 2013-01-02 09:26 -0500
            Re: pylint, was Re: pygame - importing GL - very bad... Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-01-02 23:52 +0000
              Re: pylint, was Re: pygame - importing GL - very bad... Ian Kelly <ian.g.kelly@gmail.com> - 2013-01-02 17:25 -0700
              Re: pylint, was Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-03 03:24 +0100
                Re: pylint, was Re: pygame - importing GL - very bad... Terry Reedy <tjreedy@udel.edu> - 2013-01-02 21:48 -0500
                Re: pylint, was Re: pygame - importing GL - very bad... Ian Kelly <ian.g.kelly@gmail.com> - 2013-01-02 19:55 -0700
                Re: pylint, was Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-03 12:19 +0100
                Re: pylint, was Re: pygame - importing GL - very bad... Chris Angelico <rosuav@gmail.com> - 2013-01-03 22:27 +1100
                Re: pylint, was Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-05 02:11 +0100
                Re: pylint, was Re: pygame - importing GL - very bad... Jan Riechers <janpeterr@freenet.de> - 2013-01-05 14:49 +0200
                Re: pylint, was Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-05 14:09 +0100
                Re: pylint, was Re: pygame - importing GL - very bad... Ben Finney <ben+python@benfinney.id.au> - 2013-01-03 17:01 +1100
                Re: pylint, was Re: pygame - importing GL - very bad... Chris Rebert <clp2@rebertia.com> - 2013-01-02 22:33 -0800
                Re: pylint, was Re: pygame - importing GL - very bad... Peter Otten <__peter__@web.de> - 2013-01-03 10:00 +0100
                Re: pylint, was Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-03 12:21 +0100
                Regular expression syntax, was Re: pylint, was Re: pygame - importing GL - very bad... Peter Otten <__peter__@web.de> - 2013-01-03 12:39 +0100
                Re: Regular expression syntax, was Re: pylint, was Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-05 02:12 +0100
                Re: pylint, was Re: pygame - importing GL - very bad... "Mike C. Fletcher" <mcfletch@vrplumber.com> - 2013-01-03 09:19 -0500
                Re: pylint, was Re: pygame - importing GL - very bad... Terry Reedy <tjreedy@udel.edu> - 2013-01-03 11:52 -0500
                Re: pylint, was Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-05 02:14 +0100
            Re: pylint, was Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-03 03:06 +0100
      Re: pylint, was Re: pygame - importing GL - very bad... Chris Angelico <rosuav@gmail.com> - 2013-01-03 01:32 +1100
      Re: pylint, was Re: pygame - importing GL - very bad... Ian Kelly <ian.g.kelly@gmail.com> - 2013-01-02 10:52 -0700
      Re: pylint, was Re: pygame - importing GL - very bad... Chris Angelico <rosuav@gmail.com> - 2013-01-03 04:57 +1100
      Re: pylint, was Re: pygame - importing GL - very bad... Ian Kelly <ian.g.kelly@gmail.com> - 2013-01-02 12:31 -0700
        Re: pylint, was Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-03 03:31 +0100
          Re: pylint, was Re: pygame - importing GL - very bad... Dave Angel <d@davea.name> - 2013-01-02 21:56 -0500
            Re: pylint, was Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-05 02:23 +0100
  Re: pygame - importing GL - very bad... alex23 <wuwei23@gmail.com> - 2013-01-01 14:39 -0800
    Re: pygame - importing GL - very bad... someone <newsboost@gmail.com> - 2013-01-02 00:56 +0100

csiph-web