Is it bad to use instance methods to organize code in a large python class

Question

Below I have a dummie code, where instance methods are definied mainly for code organization. The init function sets up a chain of calls to the various instance methods in a specific order, and I am just starting to feel it is bad practice to have code organized in such a way.

If so are there any references on organizing large classes (such as those found in GUI apps) to improve their readability?

Dummie code:

class App:
    def __init__(self):
        def do_things()

    def do_things(self):
        self.do_a_thing()
        self.do_another_thing()

    def do_a_thing(self):
        self.thing1 = 1    

    def do_another_thing(self):
        self.thing2 = self.thing1 + 1

These functions will only execute once when the class is called, so does that suggest they should not be functions (or instance methods)?

A working example where I have chosen this potentially bad method of organization

Below, the fill() method is akin to do_things(), and e.g. init_scroll() and init_lb() are akin to do_a_thing() and do_another_thing(), etc.

import Tkinter as tk
import tkFont

class EditorApp:
    def __init__( self, master) :
        self.root = master
        self.root.title('Editor')
        self.main = tk.Frame( self.root )
        self.main.pack(fill=tk.BOTH, expand=True)

        self.fill()

##################
# ADDING WIDGETS #
##################
    def fill( self): 
        self.canvas = tk.Canvas( self.main )
        self.canvas.pack(fill=tk.BOTH, expand=tk.YES)
        self.init_scroll()
        self.init_lb()
        self.pack_config_scroll()
        self.pack_bind_lb()
        self.fill_listbox()

##############
# SCROLLBARS #
##############
    def init_scroll(self):
        self.scrollbar  = tk.Scrollbar(self.canvas, orient="vertical")
        self.xscrollbar = tk.Scrollbar(self.canvas, orient="horizontal")

    def pack_config_scroll(self):
        self.scrollbar.config(command=self.lb.yview)
        self.xscrollbar.config(command=self.xview)
        self.scrollbar.pack(side="right", fill="y")
        self.xscrollbar.pack(side="bottom", fill="x")

    def onMouseWheel(self, event):
        self.lb.yview("scroll", event.delta,"units")
        return "break"

    def xview(self, *args):
        self.lb.xview(*args)

################
# MAIN LISTBOX #
################
    def init_lb( self):
        self.lb = tk.Listbox(self.canvas, 
                            font=tkFont.Font(self.canvas, 
                                             family="Courier", 
                                             size=14),
                            yscrollcommand=self.scrollbar.set,   
                            xscrollcommand=self.xscrollbar.set, 
                            exportselection=False)

    def pack_bind_lb(self):
        self.lb.pack(fill="both", expand=True)
        self.lb.bind("<MouseWheel>", self.onMouseWheel)

    def fill_listbox(self):
        dummie_lines = [ 'line%d\t'%x+ ''.join(['AllWorkAndNoPlayMakesJackADullBoy']*100) for x in xrange(50) ]
        for line in  dummie_lines:
            self.lb.insert(tk.END, line) 

if __name__ == '__main__':
    root   = tk.Tk()
    editor = EditorApp(root)
    root.mainloop()

I have attempted to group similar methods together for the sake of debugging (the code I pulled this from is a class which is 300 lines), but I do not know a lot about the accepted style guidelines.

Also, the full application is posted here

[You might find this interesting](http://www.pythoncentral.io/difference-between-staticmethod-and-classmethod-in-python/) — NightShadeQueen, Jul 18 '15 at 00:35
You might get a better response on codereview if the code is working and you want to improve it. — Padraic Cunningham, Jul 18 '15 at 00:40

matthewatabet · Accepted Answer · 2015-07-18T00:53:57.667

2

Is your concern that developers may call do_thing independent of do_things? While Python doesn't support private methods, you can indicate that do_thing should be treated as private by using the leading underscore convention:

def _do_thing(self):
    ...

This tells developers not to call _do_thing directly.

Generally, it's a very good idea to break large methods or functions into smaller, more manageable ones. This can be especially important when unittesting code.

edited Jul 18 '15 at 00:53

answered Jul 18 '15 at 00:31

matthewatabet

1,463
11
26

Yes, this is one potential concern. Also, I am unfamiliar with most accepted practices. Thanks for the info – dermen Jul 18 '15 at 00:33
@dermen -- great. Do you have other concerns besides best practices and protecting private methods? – matthewatabet Jul 18 '15 at 00:35
A private method has two leading underscores – Padraic Cunningham Jul 18 '15 at 00:42
@PadraicCunningham -- double underscores are not private either. But, double underscores have significant disadvantages (not being able to overload them in subclasses being one), so single underscore gets the idea across most of the time. – matthewatabet Jul 18 '15 at 00:44
They are in the context of what you are talking about in your answer – Padraic Cunningham Jul 18 '15 at 00:44
1

@PadraicCunningham -- again, no. See this answer: http://stackoverflow.com/questions/1641219/does-python-have-private-variables-in-classes – matthewatabet Jul 18 '15 at 00:45
1

http://stackoverflow.com/questions/70528/why-are-pythons-private-methods-not-actually-private You used the word private, I am well aware they can still be accessed. – Padraic Cunningham Jul 18 '15 at 00:46
To be precise -- I simply mentioned that python does not have private methods. – matthewatabet Jul 18 '15 at 00:48
*do_thing is effectively private*, badly worded then. – Padraic Cunningham Jul 18 '15 at 00:50
Thanks guys, this conversation presented a lot of useful links. – dermen Jul 18 '15 at 01:39
I am going to accept this answer. Also, I posted the full code on codereview here http://codereview.stackexchange.com/questions/97332/tkinter-gui-for-making-very-simple-edits-to-pandas-dataframes – dermen Jul 20 '15 at 21:32

Is it bad to use instance methods to organize code in a large python class

Dummie code:

A working example where I have chosen this potentially bad method of organization

1 Answers1