Instantiating classes is in general not a performance issue in Python. Your issue here strongly sounds like you're abusing OO to pass a list of instances into every method and downstream call (not just the usual reference to self, the instance at hand). Don't do that, it shouldn't be necessary. It sounds like you're trying to get a poor-man's imitation of classmethods, without identifying and refactoring whatever it is that methods might need to access from other instances.

Please post your code snippet on StackOverflow ([python] tag) or CodeReview.SE so people can help you fix it.

> created a new class with the names of each field and helper methods to process the data. The new code created a list of instances of my class. Downstream consumers of the list could look at the class to see what data they were getting.