Re: [pygame] Declaring variables in function as if at code's line-level

[Lee Buckingham <lee.buckingham@xxxxxxxxx>]

I believe so.  Just don't say something like:

def something():
     font = 1

...not that you would, but if for whatever reason it happened, you
would have created a fuction variable called 'font'  and the global
namespace would be ignored because of it.

(Do I have this right, guys?)


-Lee-



On Sat, Mar 10, 2012 at 9:34 PM, Nick Arnoeyts <nickarnoeyts@xxxxxxxxx> wrote:
> I have a little additional question about the explanation Lee gave.
>
> Is it possible to use class instances from the global namespace in a
> function? For example:
>
> from game import screen, font
>
> def get_text(string):
>     font.render(string) # parts cut out because I'm in a hurry
>
> I figure this is probably possible, but it can't hurt to ask for future
> reference.
>
>
>
>
> Op 11 maart 2012 06:13 schreef Lee Buckingham <lee.buckingham@xxxxxxxxx> het
> volgende:
>
>> Just to add a little more to Julian's response:
>>
>> in a function, you can refer to a global variable without using the
>> global keyword, like this:
>>
>> a = 1
>>
>> def something()
>>     if a == 1:  print("sure does!")
>>
>> #later on
>> something()
>> # output prints "sure does!"
>>
>>
>> On the other hand, you cannot **set it equal to something** without
>> using the global keyword.  Python is designed to assume you are making
>> a new, function-level variable that happens to have the same name.
>>
>> #this fails
>>
>> a = 1
>>
>> def something()
>>     a = 2
>>
>> #later on
>> something()
>> print(a)
>>
>> #the output will say "1"
>>
>>
>> This could have gone either way, I suppose.  The authors of python
>> could have had the interpreter do it the way you are suggesting.   If
>> I type "a=whatever", the interpreter could look up to the next scope,
>> or to the highest (line level) scope, etc... and use any like-named
>> variable first.  This could work.
>>
>> The problem is that in this situation, you would have to use something
>> like a "local" keyword every time you did NOT want to worry about the
>> possibility of accidentally naming a variable the same thing as some
>> other variable in a higher scope, like the line level variables
>> yourself and other coders prefer.
>>
>> As it turns out, the intent of the python designers favored the first
>> way, so that they could relax a bit about variable names (a lot of us
>> use variables named x, y, i, a, b, etc.., all the time, throughout the
>> code).  However, for the times when we really want to look outside a
>> function, just saying "global x" once, at the beginning of a function,
>> works just fine.
>>
>> There really are debugging issues both ways.  I have beat myself
>> senseless trying to figure out why my functions seem ineffective
>> before finally (days later) realizing I just forgot a global
>> statement.  I avoid this now, for the most part, by using a lot of
>> classes and objects, which is just a preference on my part (and it
>> drives my brother crazy).  From the other perspective, I can imagine a
>> similar problem with your favored approach, where I get ghost-changes
>> to variables on the game level for no obvious reason.  Days later,
>> after bruising my forehead and keyboard, I might notice that I named a
>> function level variable the same thing as a line level variable.  In
>> my case, this would be much, much more frustrating, since I am not
>> very creative with variable names.
>>
>> I really hope this helps a bit.  Python is a very friendly language,
>> but like all languages, is sort of slanted in certain directions of
>> its own.  I found myself repeatedly frustrated and irrate about the
>> design of VB.NET, C#, and Java, for instance.  For me, python solved
>> my problems because I think the same way.  There's nothing wrong with
>> preferring one over the other; it's just our nature, I suppose.
>>
>> Good luck with your coding!
>>
>> All the best,
>>
>> -Lee-
>>
>> On Sat, Mar 10, 2012 at 8:31 PM, Julian Marchant <onpon4@xxxxxxxxx> wrote:
>> >
>> > I am struggling with my desire to say things that would be insulting to
>> > you.
>> >
>> > Listen closely: you CAN read global-level variables at any time as long
>> > as there isn't a local variable with the same name. You CAN write to global
>> > variables from within a function as long as you first declare it within that
>> > function with the ``global`` keyword. You CANNOT write to global variables
>> > without using ``global``. The reason for this is simple: if you don't use
>> > ``global``, the interpreter assumes that you are assigning to a local
>> > (function-level) variable.
>> >
>> > Frankly, I don't see what the big deal is. It's just ONE extra line per
>> > funtion per variable that you have to write to. Consider:
>> >
>> > #!/usr/bin/env python
>> >
>> > a = > b = 0
>> > c = 0
>> >
>> > def foo():
>> >    global a
>> >
>> >    a += 1
>> >    if a > b:
>> >        a = 0
>> >
>> > def bar():
>> >    global b
>> >    global c
>> >
>> >    b = a + 10
>> >    c += a
>> >
>> >    if c > a + b:
>> >        c = 0
>> >
>> > See how easy that is? You're making a big fuss over nothing.
>> >
>> > --- On Sun, 3/11/12, Brian Brown <brobab@xxxxxxxxx> wrote:
>> >
>> >> From: Brian Brown <brobab@xxxxxxxxx>
>> >> Subject: Re: [pygame] Declaring variables in function as if at code's
>> >> line-level
>> >> To: pygame-users@xxxxxxxx
>> >> Date: Sunday, March 11, 2012, 12:15 AM
>> >> "line-level" is leftmost of the
>> >> source code.
>> >> (I thought my example code would clarify that.)
>> >> My question is very clear, I think, I'm not sure why you
>> >> guys are
>> >> having so much difficulty understanding it.
>> >> Sorry about that. I'm not trying to frustrate you, I just
>> >> wish people
>> >> would answer my questions.
>> >> (I rarely get good answers on these mailing lists. I guess I
>> >> made a
>> >> mistake asking here.)
>> >> Haven't I just given you one of the most profound statements
>> >> of
>> >> efficient game programming?
>> >> Shouldn't you be grateful? Thank you for all your replies
>> >> everyone I
>> >> guess I'm not wanted here.
>> >>
>> >>
>> >> On 3/10/12, Brian Brown <brobab@xxxxxxxxx>
>> >> wrote:
>> >> > That is not true, Ryan. I am currently making a game
>> >> with Python and
>> >> > Pygame, and my question is directly related with its
>> >> development.
>> >> >
>> >> > On 3/10/12, Ryan Hope <rmh3093@xxxxxxxxx>
>> >> wrote:
>> >> > Why is this even be talked about on the pygame ml?
>> >> This has nothing to
>> >> > do with pygame.
>> >> >
>> >> > On Sat, Mar 10, 2012 at 6:30 PM, Brian Brown <brobab@xxxxxxxxx>
>> >> wrote:
>> >> >> Hi pygame users, just a simple question-- How
>> >> can one cause variables
>> >> >> at "function-level" to behave like variables at
>> >> "line-level"? (With
>> >> >> basic python code) I just want to avoid using
>> >> "global" over and over
>> >> >> again (in many different functions) while I
>> >> want to declare, use, and
>> >> >> delete all my game's variables inside
>> >> functions.Thanks.
>> >> >>
>> >> >> It should make my program very simple and
>> >> straight-forward if I could
>> >> >> do this. (As I have explained in the previous
>> >> replies to this thread)
>> >> >> I would like to know how it can be done--
>> >> without immature,
>> >> >> unproductive statements like:
>> >> >> "Don't freak out at the fact that I used the
>> >> "class" keyword."
>> >> >> Thank you.
>> >> >>
>> >> >> Matt
>> >> >>
>> >> >> On 3/10/12, Brian Brown <brobab@xxxxxxxxx>
>> >> wrote:
>> >> >> That is not true, Chris.
>> >> >>
>> >> >> On 3/10/12, Christopher Arndt <chris@xxxxxxxxxxxxx>
>> >> wrote:
>> >> >>> On 10.03.2012 23:35, Christopher Night
>> >> wrote:
>> >> >>>     DO:
>> >> >>>     * Access variables.
>> >> >>>       (Move game according to
>> >> current-variable-status and
>> >> >>> player-input)
>> >> >>>
>> >> >>>     * Output to graphics and
>> >> sound card.
>> >> >>>       (Display game according to
>> >> current-variable-status.)
>> >> >>>     LOOP
>> >> >>>
>> >> >>>     That's really all we need.
>> >> >>>
>> >> >>> Who's this "we"? Certainly doesn't
>> >> include me, because I need *a lot*
>> >> >>> more from a programming language.
>> >> >>>
>> >> >>> Brian, I think you should read a bit
>> >> about namespaces and why they are
>> >> >>> a
>> >> >>> good thing. You won't get very far with
>> >> Python with your point of view
>> >> >>> -
>> >> >>> or in any other programming language
>> >> for that matter (except maybe PHP
>> >> >>> -
>> >> >>> just kidding ;) ).
>> >> >>>
>> >> >>>
>> >> >>> Chris
>> >> >>>
>> >> >>
>> >> >
>> >> >
>> >> >
>> >> > --
>> >> > Ryan Hope, M.S.
>> >> > CogWorks Lab
>> >> > Department of Cognitive Science
>> >> > Rensselaer Polytechnic Institute
>> >> >
>> >> >
>> >>
>> >
>
>