Re: [Pythonmac-SIG] Porting a Tkinter application to Cocoa: question about datatypes

[Ronald Oussoren]

On 13 Jun, 2007, at 8:03, Kevin Walzer wrote:

I'm looking at the possibility of porting a Tkinter-based application to

Cocoa, and since my app is already written in Python, PyObjC is the
logical starting point for me. However, what I'm not sure about is how

datatypes. For instance, the code below reads data as a list, massages
the data a bit, then returns a tuple that is then inserted into a
Tkinter table display.

             if self.catname == 'All':
                 self.catlist = os.popen('/sw/bin/fink list', 'r',
os.O_NONBLOCK)
             else:
                 self.catlist = os.popen('/sw/bin/fink list
--section=%s' % self.catname, 'r', os.O_NONBLOCK)
             for line in self.catlist:
                 newline = line.split('\t')
                 rawcat = newline[0]
                 if rawcat == '(i)':
                     firstcat=rawcat.replace('(i)', 'outdated')
                 elif rawcat == ' i ':
                     firstcat=rawcat.replace('i', 'current')
                 elif rawcat == ' p ':
                     firstcat=rawcat.replace('p', 'provided')
                 else:
                     firstcat = rawcat
                 newlist = (firstcat, newline[1], newline[2],
newline[3].strip('\n')) #finalline)
                 self.infotable.insert('end' , newlist)

Except for the line "self.infotable.insert('end' , newlist)", there is
nothing Tkinter-specific in this code.

If I used Interface Builder for the table view, would this data import

datatype (NSMutableArray?) to parse and display the data correctly? If
so, how could this snippet be rewritten?

much translation I'd have to do between Python datatypes and Objective-C cleanly into the GUI, or would I have to set up some sort of NS- prefixed

There is a tablemodel example included with PyObjC.

Python lists, tuples and dictionaries are proxied using a subclass of the corresponding NS* type. You almost never have to use the NS* types explictly. The major exception to this is Key-Value Observing (also known as Cocoa bindings). Cocoa bindings requires that objects emit events when they are mutated (append an item, set the value for a key in a dict, ...). Sadly enough Python doesn't have the hooks that are required to emit these events for pure python objects. Adding this support requires some low-level changes to python and I'm not sure if this can be done without adversely affecting the performance of the interpreter.

My preference in porting my application is to refactor the GUI layer
from Tkinter to PyObjC, but otherwise retain as much of my code as
possible in its present (Python-generic) form. Is this a feasible

mindset, designing the entire app from the top down to use
NS*-datatypes? That's a lot more work and I might as well learn
Objective-C and just use that.

approach, or does using PyObjC require adopting more of an "Objective-C"

Ronald

Learning a little Objective-C might not be a bad idea anyway, you can find a lot of examples and code snippets on the web and most of those are written in ObjC. The major reasons for not switching to ObjC are the normal reasons for liking Python over compiled languages and the enormous amount of libraries available in Python. Something like Twisted beats all available networking libraries for Cocoa with a huge margin and simular advantages are available for other use cases.

TIA,
Kevin

--
Kevin Walzer
Code by Kevin
http://www.codebykevin.com
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