Correct use of static methods

Question

I have following simplified class named Password.py in folder1:

import random CHARS = "ABC" class PasswordHelper(object): @staticmethod def generateChars(length): return ''.join(random.choice(CHARS) for x in range(length))

Now I have another class TestClass.py in folder2:

sys.path.append('../folder1/') import Password class Tester: def whatever(self): print Password.generateChars(3) def main(): x = Tester() x.whatever() # call main method main()

When calling python TestClass.py I get the following error: AttributeError: 'module' object has no attribute 'generateChars'. Both folders are on the same level. Is there a problem with the way I import the class files or with the static method declaration itself?

Daniel Roseman · Accepted Answer · 2012-11-03 17:20:32Z

Python is not Java.

Firstly, there is absolutely no point to either the Tester or the Password classes. If you're not storing state, then don't define a class. Make both whatever and generateChars into normal standalone functions.

However, assuming you're doing this just to learn about Python classes, you have not understood that a class does not equal a module in Python. Since you've imported the Password module, you still need to refer to the PasswordHelper class:

Password.PasswordHelper.generateChars(3)

Alternatively, you can import the PasswordHelper class:

from Password import PasswordHelper ... PasswordHelper.generateChars(3)

Finally, please follow PEP8 for your module, class and function names.

+1 NB even if you have state it may make sense to pass that state around as arguments and return values. But that's a matter of taste, first get rid of the "classes for everything" mindset.
Hmm. Alright. I seriously thought that having a class for everything was considered good style. I guess I was wrong...
Actually I'm wondering, why exactly it is bad to have classes for everything? Are there more "deeper" readings to it?
@cherrun You should read Python is not Java, it also raises other issues. My personal problem with classes for everything is that it's plain pointless: It just adds another element to the picture which doesn't have any use, but wastes screen space, mental capacity, needs a name (which has to be remembered), etc. -- and it indicates that the programmer is unaware of paradigms beside OOP and their use (or, even worse, shuns them for bad/invalid reasons).

Martijn Pieters · Accepted Answer · 2012-11-03 17:18:18Z

You defined the function in a class, so you need to reference it with the classname too:

print Password.PasswordHelper.generateChars(3)

Alternatively, move the function out of the class definition, at which point you do not need to use @staticmethod at all:

import random CHARS = "ABC" def generateChars(length): return ''.join(random.choice(CHARS) for x in range(length))

In Python, functions do not have to be part of a class definition.

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