[Tutor] More OOP

Tim Ronning tim.ronning at start.no
Mon Nov 10 13:47:28 EST 2003

På Fri, 7 Nov 2003 19:42:43 -0000, skrev Alan Gauld 
<alan.gauld at blueyonder.co.uk>:

> Its not necessary but there is a natural synergy between GUI widgets
> and objects. Also many GUI toolkits are implemented as object
> frameworks
> so you have to use objects anyway, you might as well make your code
> fit in.

The attached code is a new little learning project of mine. And it somewhat 
ilustrates what I meant with "learning GUI" straight away. I think the code 
(albeit small) is fairly OO (correct me if I'm wrong). And it felt natural 
somehow to devide things into functions and a class and work with 
attributes of an object(instance). I know that if I had done this without a 
GUI I would have gone with batch style (the old autoexec.bat is haunting 
me!) So to the question, is this more difficult to learn? Or is it just 
moore to learn? I think, if you have good tools like 
QTDesigner+Eric/Blackadder or wxPython+wxGlade or pyfltk+flconvert, one can 
go GUI quite soon in ones learningprocess without overloading oneself with 
new stuff to learn. It took me 5 minutes to generate the FLTK GUI code in 
this script, and going through it, line by line, it's fairly easy to 
understand what each line do, even for a novice like myself. The concepts 
behind the core Python lines are a bit more difficult to learn, but for me 
personally I think the GUI portion helps me understand the Python objects 
because it introduces the concepts of object attributes(methodes). And 
somehow these attributes makes more sense when I can fixate them to visible 
widgets. Maybe it's just me?
Anyway, here's the Python/FLTK code for a simple product/VAT calculator.

Best regards
Tim R.
#!/usr/bin/env python
# -*-coding: iso-8859-1 -*-

from fltk import *
import sys

# global object names
window_main = None      # type 'Fl_Window' from 'make_window()'
gross_pris = None      # type 'Fl_Value_Input' from 'make_window()'
outp_umoms = None      # type 'Fl_Value_Output' from 'make_window()'
outp_mmoms = None      # type 'Fl_Value_Output' from 'make_window()'
outp_inntj = None      # type 'Fl_Value_Output' from 'make_window()'
outp_skyldig = None      # type 'Fl_Value_Output' from 'make_window()'
kalk_knapp = None      # type 'Fl_Button' from 'make_window()'
logo = None      # type 'Fl_Box' from 'make_window()'
pris_u_moms = 0
pris_m_moms = 0
inntjening = 0
skyldig_moms = 0
verdi = 0

def createobj(ptr):
     global pris_u_moms, pris_m_moms, inntjening, skyldig_moms
     i = Productcalc(verdi)
     pris_u_moms = i.umoms()
     pris_m_moms = i.mmoms()
     inntjening = i.inntj()
     skyldig_moms = i.skyldig()

def getValue(ptr):
    global verdi
    valuator = castWidget2Valuator(ptr)
    verdi = valuator.value()
    return verdi

def make_window():
    global window_main
    global gross_pris
    global outp_umoms
    global outp_mmoms
    global outp_inntj
    global outp_skyldig
    global kalk_knapp
    global logo

    window_main = Fl_Double_Window(404, 471, 308, 235, 

    gross_pris = Fl_Value_Input(100, 40, 90, 25, """Gross. price""")
    gross_pris.label('''Gross. price''')

    outp_umoms = Fl_Value_Output(100, 75, 90, 25, """Price ex. vat""")
    outp_umoms.label('''Price ex. vat''')

    outp_mmoms = Fl_Value_Output(100, 110, 90, 25, """Customer""")

    outp_inntj = Fl_Value_Output(100, 145, 90, 25, """Profit""")

    outp_skyldig = Fl_Value_Output(100, 180, 90, 25, """VAT to pay""")
    outp_skyldig.label('''VAT to pay''')

    kalk_knapp = Fl_Button(205, 40, 90, 25, """Calculate""")

    logo = Fl_Box(50, 5, 215, 25, """Productcalculations v. 0.1.0""")
    logo.label('''Productcalculations v. 0.1.0''')

    return window_main

class Productcalc:
     def __init__(self, g_pris):
          self.g_pris = g_pris
     def umoms(self):
          return self.g_pris+(self.g_pris*0.35)
     def mmoms(self):
          return (self.g_pris+(self.g_pris*0.35))*1.24
     def inntj(self):
          return (self.g_pris*0.24)+((self.g_pris+(self.g_pris*0.35))- 
     def skyldig(self):
          return (((self.g_pris+(self.g_pris*0.35))*1.24)- 

if __name__=='__main__':
    window = make_window()
    window.show(len(sys.argv), sys.argv)

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