Python Class vs. Module Attributes

Question

I\'m interested in hearing some discussion about class attributes in Python. For example, what is a good use case for class attributes? For the most part, I can not come up

Answer 1

what is a good use case for class attributes

Case 0. Class methods are just class attributes. This is not just a technical similarity - you can access and modify class methods at runtime by assigning callables to them.

Case 1. A module can easily define several classes. It's reasonable to encapsulate everything about class A into A... and everything about class B into B.... For example,

# module xxx
class X:
    MAX_THREADS = 100
    ...

# main program
from xxx import X

if nthreads < X.MAX_THREADS: ...

Case 2. This class has lots of default attributes which can be modified in an instance. Here the ability to leave attribute to be a 'global default' is a feature, not bug.

class NiceDiff:
    """Formats time difference given in seconds into a form '15 minutes ago'."""

    magic = .249
    pattern = 'in {0}', 'right now', '{0} ago'

    divisions = 1

    # there are more default attributes

One creates instance of NiceDiff to use the existing or slightly modified formatting, but a localizer to a different language subclasses the class to implement some functions in a fundamentally different way and redefine constants:

class Разница(NiceDiff): # NiceDiff localized to Russian
    '''Из разницы во времени, типа -300, делает конкретно '5 минут назад'.'''

    pattern = 'через {0}', 'прям щас', '{0} назад'

Your cases:

• constants -- yes, I put them to class. It's strange to say self.CONSTANT = ..., so I don't see a big risk for clobbering them.
• Default attribute -- mixed, as above may go to class, but may also go to __init__ depending on the semantics.
• Global data structure --- goes to class if used only by the class, but may also go to module, in either case must be very well-documented.