Question

I have a class which contains a number of class variables:

c_dict1, c_dict2, c_dict3

They are all dictionaries, and store some values using some of the instance variables below as keys.

I have a few hundreds of instances of this class, and each has the following instance variables:

i_key1, i_key2, i_key3, i_attr1, i_attr2, i_attr3

They first three (i_key*) can be used to look up the latter three (i_attr*) in the class variables. In other words:

self.i_attr1 = MyClass.c_dict1(i_key1)
self.i_attr2 = MyClass.c_dict2(i_key2)
self.i_attr3 = MyClass.c_dict3(i_key3)

My question is:

In terms of performance, should I maintain the instance variables i_attr* locally, or should I access them via dictionary lookup using class variables c_dict*? Obviously, doing via the class variables get rid of three pointers per instance, which may save some memory, but is there any significant speed penalty for doing it this way?

Answer 1

In terms of performance, should I maintain the instance variables i_attr* locally, or should I access them via dictionary lookup using class variables c_dict*?

If this sort of constant-time micro-optimisation is important and not premature, probably don’t use python.

I strongly suspect that this is premature optimisation, and you have not identified this as a hotpot, because if you had, you could just profile your code both ways, and wouldn’t be asking here.

You can get much more of a speedup by worrying about your architecture, whether you should be running a long-lived process which can take advantage of PyPi, etc.