function that run once for all objects

[deanhystad]

I think having the __init__ method check a class variable should work great for this.

class Thing:
    parameters = None  # Stuff you want to read once and use many times

    @classmethod
    def init_parameters(cls):
        '''Load parameters from a file. All instances will share these parameters'''
        # Open file an read parameters
        cls.parameters = whatever()

    def __init__(self):
        if self.parameters is None:
            self.init_parameters()  # Initialize these class variables from a file.  Happens once.
        #Can use the parameters now

Sounds like all instances will share these parameters, so it makes sense to use a class variable to reference them.

If this is not applicable to your problem, why not? Can you explain please.