Distinguishing different types of class attributes

[deanhystad]

I don't use class variables very often.

Here I used class variables to define some constants that are used by instances of the class.

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class Message:     """A class for sending and receiving XXXX style messages.     My most used methods are:     send_message - Send message to remote process     recv_ reply - Get reply from sent message     recv_message - Read asynchronous message from a remote process     send_reply - Send reply to remote process     """     sentinel = 0xF1F2F3F4  # Value used to mark start and end of a message     max_params = 8  # Number of parameters in message     typestr_size = 16  # Size for argument typestring in message     selector_size = 32  # Size for selector string in message

Here I use a class variable to keep a list of all instances of the class.

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class Model(XXXX):     instances = []       def __init__(self, parent=None, link=None):         super().__init__()         self.parent = parent         self._link = link         self.parts = []         self.instances.append(self)

I can use Model.instances to count how many instances of the class were created, to execute an instance method for each instance, to delete all instances, to keep all instances from being garbage collected.

I've seen code from other Python programmers who use class variables fairly frequently. I remember one poster on this forum who used classes as namespaces. All the variables in his classes were class variables, and all of his classes were singletons.

Class variables are a language feature and it is really up to you to decide when the are useful. Your problem space is not the same as mine. How I write Python is not how you should write Python.