Learning Tkinter

Eric Brunel see.signature at no.spam
Thu Apr 17 13:48:38 CEST 2008


On Wed, 16 Apr 2008 14:46:13 +0200, Doran, Harold <HDoran at air.org> wrote:
[snip]
> Second, I am trying to work through a couple of the examples and make
> some small tweaks as I go to see how new things can work. In the first
> case, I have copied the code in the book to see how the menu works and
> are created as in the example menu.py below. I see how menus are created
> and how the command option is used to call the function callback.
>
> # menu.py
> from Tkinter import *
>
> def callback():
>     print "called the callback!"
>
> root = Tk()
>
> # create a menu
> menu = Menu(root)
> root.config(menu=menu)
>
> filemenu = Menu(menu)
> menu.add_cascade(label="File", menu=filemenu)
> filemenu.add_command(label="New", command=harold)
> filemenu.add_command(label="Open...", command=callback)
> filemenu.add_separator()
> filemenu.add_command(label="Exit", command=callback)
>
> helpmenu = Menu(menu)
> menu.add_cascade(label="Help", menu=helpmenu)
> helpmenu.add_command(label="About...", command=callback)
>
> mainloop()
>
> However, I now want to incorporate a basic python program with a
> command. Say I have a simple program called test.py
>
> # test.py
> filename = raw_input("Please enter the file you want to open: ")
> new_file = raw_input("Save the output file as: ")
>
> f = open(new_file, 'w')
> new = open(filename, 'r')
>
> for line in new:
> 	x = line.split('\t')
> 	print >> f, x[0],':', x[1]
> f.close()
>
> To make this example complete assume I have a text file like this
>
> # data.txt
> 1	one
> 2	two
> 3	three
> 4	four
>
> So, the user currently just follows directions on the screen, enters the
> file names, and I get what I want. I'd like to try experimenting with
> gui programming to see if the python programs I have written can be made
> even more user friendly. I currently use py2exe to create executables so
> that others in my organization can use these programs.
> In that spirit, say I want to have a menu option that allows the user to
> search their computer for this file, execute the python code and then
> save the result as a user-defined filename. So, I guess my questions are
> how do I associate the portion of code in menu.py
> "filemenu.add_command(label="Open...", command=callback)" with an
> operation that gives the user the ability to search the drives on their
> machine and then once they do let python execute the code in test.py?

The way it's written, you'll have a hard time doing it... Since test.py  
already includes a "user interface" via the raw_input calls, executing  
test.py will always ask the user for the file names, and there's no simple  
way to pass them otherwise as the module is written.

Considering how you asked the question, I'll assume you don't know Python  
very much; my apologies in advance if it's not the case...

So, what I would do is rewrite the test.py script as follows:

--- test.py -----------------------------------
def convert_file(filename, new_file):
   f = open(new_file, 'w')
   new = open(filename, 'r')

   for line in new:
     x = line.split('\t')
     print >> f, x[0],':', x[1]
   f.close()

if __name__ == '__main__':
   filename = raw_input("Please enter the file you want to open: ")
   new_file = raw_input("Save the output file as: ")
   convert_file(filename, new_file)
-----------------------------------------------

This is basically the same as yours in another order, and defining a  
function that actually does the 'functional' part without asking the user  
anything. The last block - starting with this weird 'if __name__ ==  
'__main__':' - ensures the script will work as you expect when you run it  
alone on the command line (with 'python test.py'). This is the meaning of  
the test on __name__: this magical variable is set to the string  
'__main__' if and only if the current script is the top-most one, i.e the  
one you ran python on. So basically, the script now defines a function,  
then asks for the function parameters and calls it _only if run as the  
main script_. Try it; it should have the same behaviour as the script  
you've written.

But the test on __name__ also allows to *import* this script as a module  
in another script without nasty side effects. This is done via the  
statement:

import test

in the other script. If test.py is written as above, this will execute the  
function definition, but not the body of the 'if', since test.py is no  
more run from the command line, but used in an import. If you didn't have  
this test, the module would have been *executed* by the import, and is  
would have asked the file names immediatly.

Once you've done the import, you can then use the function it defines by  
calling test.convert_file. So now, in your GUI part, you can now write  
something like:


--- menu.py ----------------------------------
## NEW! the next line gets the 'convert_file' function
import test
 from Tkinter import *
## NEW! the next line gets the functions used to get file names via a  
Tkinter GUI
 from tkFileDialog import askopenfilename, asksaveasfilename

## NEW! the following function is the callback for the 'Open' menu entry
def open_callback():
   ## Get name of the input file
   input_file_name = askopenfilename()
   if not input_file_name:
     ## Dialog has been cancelled
     return
   ## Get name for output file
   output_file_name = asksaveasfilename()
   if not output_file_name:
     ## Dialog has been cancelled
     return
   ## Do the job
   test.convert_file(input_file_name, output_file_name)

def callback():
   print "called the callback!"

root = Tk()

# create a menu
menu = Menu(root)
root.config(menu=menu)

filemenu = Menu(menu)
menu.add_cascade(label="File", menu=filemenu)
filemenu.add_command(label="New", command=harold)
## CHANGED! put the callback function defined above here
filemenu.add_command(label="Open...", command=open_callback)
filemenu.add_separator()
filemenu.add_command(label="Exit", command=callback)

helpmenu = Menu(menu)
menu.add_cascade(label="Help", menu=helpmenu)
helpmenu.add_command(label="About...", command=callback)

mainloop()
----------------------------------------------

Try it: it should basically do what you were asking for.

HTH
-- 
python -c "print ''.join([chr(154 - ord(c)) for c in  
'U(17zX(%,5.zmz5(17l8(%,5.Z*(93-965$l7+-'])"



More information about the Python-list mailing list