Using globals with classes

**Diez B. Roggisch** · Aug 12 '05, 08:35 AM

Re: Using globals with classes

[color=blue]
> Is there a way to make a Python function "remember" the values of certain
> variables ? Or use fortran 95 like use module, only : varname, type of
> within a def ?[/color]

I'm not sure what you are trying to do here - but it seems to me that
you are not properly designing your application. You really shouldn't
use the Designers code-insertion features. The reason is simple: you
the have two tools to write code in instead of one (your editor/IDE).
And you don't make plotkey* global - use instance variables.

So I'm going to describe how I dow work with PyQt:

- I create a Widget in the designer
- compile it using pyuic
- _extend_ it
- write my code in the extended version

So I end up with something like this (I use modules to separate
classes):

ui/plot.ui
ui/plot.py
views/plot.py

where views/plot.py looks like this:

class Plot(ui.plot.Pl ot):
def __init__(self, *args):
ui.plot.Plot.__ init__(self, *args)
self.plotkey1 = <whatever>

def update(self):
# access self.plotkey here

HTH,

DIez

**Diez B. Roggisch** · Aug 12 '05, 08:35 AM

Re: Using globals with classes

[color=blue]
> Is there a way to make a Python function "remember" the values of certain
> variables ? Or use fortran 95 like use module, only : varname, type of
> within a def ?[/color]

I'm not sure what you are trying to do here - but it seems to me that
you are not properly designing your application. You really shouldn't
use the Designers code-insertion features. The reason is simple: you
the have two tools to write code in instead of one (your editor/IDE).
And you don't make plotkey* global - use instance variables.

So I'm going to describe how I dow work with PyQt:

- I create a Widget in the designer
- compile it using pyuic
- _extend_ it
- write my code in the extended version

So I end up with something like this (I use modules to separate
classes):

ui/plot.ui
ui/plot.py
views/plot.py

where views/plot.py looks like this:

class Plot(ui.plot.Pl ot):
def __init__(self, *args):
ui.plot.Plot.__ init__(self, *args)
self.plotkey1 = <whatever>

def update(self):
# access self.plotkey here

HTH,

DIez

**Scott David Daniels** · Aug 12 '05, 05:45 PM

Re: Using globals with classes

Madhusudan Singh wrote:[color=blue]
> .... I am using qwtplot to display a running plot :
>
> void Form3::runningp lot(n,plottitle ,xname,x,y1name ,y1,y2name,y2)
> {[/color]
^^ I presume this is just some untranslated stuff ^^[color=blue]
> if n==1 :
>
> plotkey1=self.r unningqwtPlot.i nsertCurve(y1na me,self.running qwtPlot.xBottom ,self.runningqw tPlot.yLeft)
>
> plotkey2=self.r unningqwtPlot.i nsertCurve(y2na me,self.running qwtPlot.xBottom ,self.runningqw tPlot.yRight)
> self.runningqwt Plot.setTitle(p lottitle)
> self.runningqwt Plot.setXGrid(T rue)
> self.runningqwt Plot.setAxisAut oScale(self.run ningqwtPlot.yLe ft)
> self.runningqwt Plot.setAxisAut oScale(self.run ningqwtPlot.yRi ght)
> self.runningqwt Plot.setAxisAut oScale(self.run ningqwtPlot.xBo ttom)
> self.runningqwt Plot.setAxisTit le(self.running qwtPlot.yLeft,y 1name)
> self.runningqwt Plot.setAxisTit le(self.running qwtPlot.yRight, y2name)
> self.runningqwt Plot.setAxisTit le(self.running qwtPlot.xBottom ,xname)
> self.runningqwt Plot.setCurveDa ta(plotkey1,x,y 1,n)
> self.runningqwt Plot.setCurveDa ta(plotkey2,x,y 2,n)
> self.runningqwt Plot.replot()
> else :
> self.runningqwt Plot.setCurveDa ta(plotkey1,x,y 1,n)
> self.runningqwt Plot.setCurveDa ta(plotkey2,x,y 2,n)
> self.runningqwt Plot.replot()
> }[/color]

The way I'd normally accomplish this is to separate the setup and use
by defining a class:

class CurvePlot(objec t):
def __init__(self, plot, plottitle, xname, y1name, y2name,
key1=None, key2=None):
self.plot = plot
if key1 is None:
key1 = plot.insertCurv e(y1name, plot.xBottom, plot.yLeft)
self.key1 = key1
if key2 is None:
key2 = plot.insertCurv e(y2name, plot.xBottom, plot.yRight)
self.key2 = key2
plot.setTitle(p lottitle)
plot.setXGrid(T rue)
plot.setAxisAut oScale(plot.yLe ft)
plot.setAxisAut oScale(plot.yRi ght)
plot.setAxisAut oScale(plot.xBo ttom)
plot.setAxisTit le(plot.yLeft, y1name)
plot.setAxisTit le(plot.yRight, y2name)
plot.setAxisTit le(plot.xBottom , xname)

def curve(self, x, y1, n)
self.plot.setCu rveData(self.ke y1, x, y1, n)
self.plot.setCu rveData(self.ke y2, x, y2, n)
self.plot.replo t()

And then calling it like:

cplot = CurvePlot(self. runningqwtPlot, plottitle,
xname, y1name, y2name)
cplot.curve(n, x, y1, y2)
[color=blue]
> I also have a global variable named "globaldebu g" that when set to True,
> shows some diagnostic information as different slots are called. That too
> fails with the same error :
>
> NameError: global name 'globaldebug' is not defined[/color]
What you probably don't understand is that "globals" are per-module, not
program-wide. If you write a global from inside a function or method,
you need to declare "global varname" inside the function or method in
which you do the writing. Simply using (reading) a global in a module
does not require the "global" declaration.

--Scott David Daniels
Scott.Daniels@A cm.Org

**Madhusudan Singh** · Aug 12 '05, 09:25 PM

Re: Using globals with classes

Many thanks for an excellent solution to the problem and clearing up my mind
about globals.

In some sense, Python globals seem to be a little like the COMMON statement
in the old Fortran 77 standard.

**Madhusudan Singh** · Aug 13 '05, 09:05 PM

Re: Using globals with classes

Scott David Daniels wrote:
[color=blue]
> Madhusudan Singh wrote:[color=green]
>> .... I am using qwtplot to display a running plot :
>>[/color]
> The way I'd normally accomplish this is to separate the setup and use
> by defining a class:
>[/color]

How would one enable dynamic autoscaling of the axes ?

I am using setAxisAutoScal e, and when the application ends, I do get
correctly autoscaled axes, but not while the measurement is in progress.

**Dennis Lee Bieber** · Aug 14 '05, 01:15 AM

Re: Using globals with classes

On Fri, 12 Aug 2005 17:13:21 -0400, Madhusudan Singh
<spammers-go-here@spam.inval id> declaimed the following in
comp.lang.pytho n:
[color=blue]
>
> In some sense, Python globals seem to be a little like the COMMON statement
> in the old Fortran 77 standard.[/color]

Not really. Fortran COMMON block were named pages of memory. The
interpretation of that memory was dependent upon the variables declared
to be /in/ the COMMON block. Prior to the capability to in "include"
files, it was quite easy to make a mistake and misalign references to
COMMON.

program main

double precision a_real
integer int_array(5)
float real_2
common /some_common/ a_real, real_2, int_array

-=-=-=-=-=-

subroutine callme

double precision my_real
double precision really_2
integer my_ints(5)
common /some_common/ my_real, really_2, my_ints

-=-=-=-=-=-

a_real and my_real are okay -- same double precision
real_2 and really_2 differ in size; so really_2 is accessing half
its value from what is int_array(1).
int_array array and my_ints are both five elements long... but the
mismatch on really_2 means that my_ints (1..4) align with
int_array(2..5)

Python's "global" statement, when used inside a function/method
basically says "modify the variable defined at the module (aka, file)
level"

--[color=blue]
> =============== =============== =============== =============== == <
> wlfraed@ix.netc om.com | Wulfraed Dennis Lee Bieber KD6MOG <
> wulfraed@dm.net | Bestiaria Support Staff <
> =============== =============== =============== =============== == <
> Home Page: <http://www.dm.net/~wulfraed/> <
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Using globals with classes

Using globals with classes

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