[WxPython] Advice on Temperature Application Method & Structure

Wed May 26 08:34:06 EDT 2010

On May 26, 2010, at 7:36 AM, Jimbo wrote:

> Hello
>
> I have made a simple application using WxPython that is a temperature
> converter. This is my first application made in WxPython, the only
> other apps I have made were in Win32 c++ so I am new to widgets in
> general.
>
>
> I am looking for advice & criticism on when you should use classes in
> GUI widget apps (& where) & other general advice:

Hi Jimbo,
The first piece of advice I have is to post on the wxPython mailing  
list where you'll reach a more focused audience.

> - Should every window be in its own class?

That works for me.

> - whats the best way to refer to a control (by window name or ID)

ID. Uniqueness is not enforced among window names.

> - Should a group of controls that are related be in a class
> For example should I make a Celsius class that handles the
> celsius editbox, static & button & the button action
> function(convert_to_fahrenheit())?

When and where to use a class is not wxPython-specific, and is partly  
a matter of taste. For instance, I would not put a  
convert_to_fahrenheit() function inside a class, because it doesn't  
need any class-related info. Make it a module-level function and it  
will be easier to re-use. I wouldn't do what you suggested (grouping  
controls into a class) because it doesn't seem to serve any purpose  
other than documentation, which can be accomplished just as well with  
a comment. Ask yourself this -- what problem would grouping them into  
a class solve?

> - When & why use a Validator??

I'm ambivalent about Validators. Before I used them I had all of my  
init code in one place, and in the on_ok_clicked() event I had all of  
my teardown code and it was easy to see what control got assigned to  
which variable. Now that information is scattered through a bunch of  
classes which are fairly verbose.

Also, Validators are great for validating individual controls, but not  
so great with groups. E.g. when control A can only be blank if B is  
too. A & B have to know about one another and the Validator starts to  
get messy.

OTOH it's nice to group the code that knows everything that needs to  
be know about the relationship between a control and the variable to  
which is assigned. We call the validator when the control loses focus  
(to let users know if they've entered something invalid) and when OK  
is clicked. It's nice to be able to simply call the validators in that  
case.

Good luck with your app
Philip

> Temperature Converter Application:
> """
> Temperature Application
>
> Description: This application uses WxPython to create a simple
> windows app to convert temperature from celsius
> to fahrenheit & visa versa.
>
> Looking for advice on everything to do with wxPython:
> For example:
> - Structure of a wxPython script/code
> - Should every window be in its own class?
> - whats the best way to refer to a control (by window name or ID)
> - Should a ground of controls that are related be in a class
> For example should I make a Celsius class that handles the
> celsius editbox, static & button?
> - Errors, bad things I have done in my code
> - When & why use a Validator??
> """
>
>
> import wx
>
>
> ## Constants ##
> ID_FAHREN = 1
> ID_CELSIUS = 2
>
>
> class Controller(wx.Frame):
>
>
> def __init__(self, parent, id):
>
> wx.Frame.__init__(self,parent,id,"Temperature Converter",
> size=(247,186))
>
> # Create Controls
> panel = wx.Panel(self)
> self.create_controls( panel, wx.Validator() )
>
> self.fah_edit.SetValue(str(32))
> self.cel_edit.SetValue(str(0))
>
> # Define actions
> self.Bind_Events()
>
>
> def create_controls(self, panel, val):
> """ Create all the controls we will need for the temperature
> conversion """
>
> self.bmp_static = wx.StaticText(panel, -1, "Bitmap pic will be here",
> (10,5), (150,40))
>
> self.fah_static = wx.StaticText(panel, -1, "Fahrenheit: ",
> (10,70), (-1,-1))
>
> self.cel_static = wx.StaticText(panel, -1,"Celsius: ",
> (140,70), (-1,-1))
>
> self.fah_edit = wx.TextCtrl(panel,ID_FAHREN, pos=(70,65),
> size=(40,25), style=0, validator=val,
> name='a')
>
> self.cel_edit = wx.TextCtrl(panel,ID_CELSIUS, pos=(180,65),
> size=(40,25), style=0, validator=val,
> name='b')
>
> self.to_fah_button = wx.Button(panel,label="To Fahrenheit",
> pos=(145,95),size=(80,25))
>
> self.to_cel_button = wx.Button(panel,label="To Celsius",
> pos=(35,95),size=(80,25))
>
> self.exit_button = wx.Button(panel,label="Exit",pos=(157,123),
> size=(70,25))
>
>
>
> def Bind_Events(self):
> """ Bind application events to class functions """
>
> self.Bind(wx.EVT_BUTTON,self.close_button,
> self.exit_button)
>
> self.Bind(wx.EVT_CLOSE,self.close_window)
>
> self.Bind(wx.EVT_BUTTON,self.convert_to_celsius,
> self.to_fah_button)
>
> self.Bind(wx.EVT_BUTTON,self.convert_to_fahrenheit,
> self.to_cel_button)
>
>
> def close_button(self, event):
>
> self.Close(True)
>
>
> def close_window(self, event):
>
> self.Destroy()
>
>
> def error_check(self, string):
> """ Check for valid input in editboxes. Valid input
> includes float & integer values only """
>
> if string.isalpha() or len(string) <= 0:
>
> return False
>
> return True
>
>
> def convert_to_fahrenheit(self, event):
> """ Convert the value in fahrenheit window to celsius &
> display in our window/edit box """
>
> # Algorithm
> # - Get number from fahrenheit editbox
> # - convert fahrenheit value to celsius
> # - change value in Celsius Window to
>
> # Step 1:
> fahren_value = self.fah_edit.GetValue()
>
> if not self.error_check( fahren_value ):
>
> self.fah_edit.SetValue( "NA" )
> return
>
> # Step 2:
> value = (float(fahren_value) - 32) * 5/9
>
> # Step 3:
> self.cel_edit.SetValue( str(value) )
>
>
> def convert_to_celsius(self, event):
> """ Convert the value in celcius window/editbox to
> fahrenheit & display in our window/editbox """
>
> # Algorithm
> # - Get number from celsius editbox
> # - convert celsius value to fahrenheit
> # - change value in fahrenheit Window
>
> # Step 1:
> celsius_value = self.cel_edit.GetValue()
>
> if not self.error_check( celsius_value ):
>
> self.cel_edit.SetValue( "NA" )
> return
>
> # Step 2:
> value = (float( celsius_value ) * 9/5) + 32
>
> # Step 3:
> self.fah_edit.SetValue( str(value) )
>
>
>
> if __name__ == "__main__":
>
> app = wx.PySimpleApp()
>
> frame = Controller(parent=None,id=-1)
> frame.Show()
> app.MainLoop()
> -- 
> http://mail.python.org/mailman/listinfo/python-list