Python - Lazy loading of class attributes

Question

Class foo has a bar. Bar is not loaded until it is accessed. Further accesses to bar should incur no overhead.

class Foo(object):

    def get_bar(self):
            


        

Answer 1

Sure it is, try:

class Foo(object):
    def __init__(self):
        self._bar = None # Initial value

    @property
    def bar(self):
        if self._bar is None:
            self._bar = HeavyObject()
        return self._bar

Note that this is not thread-safe. cPython has GIL, so it's a relative issue, but if you plan to use this in a true multithread Python stack (say, Jython), you might want to implement some form of lock safety.