Grouping Functions by Using Classes in Python

Question

I have been a Python Scientific Programmer for a few years now, and I find myself coming to a sort specific problem as my programs get larger and larger. I am self taught so I h

Answer 1

I think doing so is perfectly pythonic. This is exactly the purpose of staticmethod constructor.

For python conventions, see PEP 8.

Answer 2

Another approach is to make a util package and split up your functions into different modules within that package. The basics of packages: make a directory (whose name will be the package name) and put a special file in it, the __init__.py file. This can contain code, but for the basic package organization, it can be an empty file.

my_package/
  __init__.py
  module1.py/
  modle2.py/
  ...
  module3.py

So say you are in your working directory:

mkdir util
touch util/__init__.py

Then inside your util directory, make calc_funcs.py

def add(a,b):
    return a + b

def sub(a,b):
    return a -b

And format_funcs.py:

def cap(string):
    return string.title()

def lower(string):
    return string.lower()

And now, from your working directory, you can do things like the following:

>>> from util import calc_funcs
>>> calc_funcs.add(1,3)
4
>>> from util.format_funcs import cap
>>> cap("the quick brown fox jumped over the lazy dog")
'The Quick Brown Fox Jumped Over The Lazy Dog'

Edited to add

Notice, though, if we restart the interpreter session:

>>> import util
>>> util.format_funcs.cap("i should've been a book")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'util' has no attribute 'format_funcs'

This is what the __init__.py is for!

In __init__.py, add the following:

import util.calc_funcs, util.format_funcs

Now, restart the interpreter again:

>>> import util
>>> util.calc_funcs.add('1','2')
'12'
>>> util.format_funcs.lower("I DON'T KNOW WHAT I'M YELLING ABOUT")
"i don't know what i'm yelling about"

Yay! We have flexible control over our namespaces with easy importing! Basically, the __init__.py plays an analogous role to the __init__ method in a class definition.

Answer 3

I wouldn't use a class for this, I'd use a module. A class consisting of only staticmethods strikes me as a code smell too. Here's how to do it with modules: any time you stick code in a separate file and import it into another file, Python sticks that code in a module with the same name as the file. So in your case:

In mathutil.py

def add(a,b):
    return a+b

def sub(a,b):
    return a-b

In main.py

import mathutil

def main():
    c = mathutil.add(a,b)

Or, if you're going to use mathutil in a lot of places and don't want to type out (and read) the full module name each time, come up with a standard abbreviation and use that everywhere:

In main.py, alternate version

import mathutil as mu

def main():
    c = mu.add(a,b)

Compared to your method you'll have more files with fewer functions in each of them, but I think it's easier to navigate your code that way.

By the way, there is a bit of a Python convention for naming files/modules: short names, all lower case, without underscores between words. It's not what I started out doing, but I've moved over to doing it that way in my code and it's made it easier to understand the structure of other people's modules that I've used.