python class variable update based on dictionary

Question

How can I update class variable from dictionary? I've came up with a dirty hack, but I'm looking (if there is) for something more neat.

Let's say I want a class C which parameters will be set based on given dictionary. As a result, c should have

class C:
    def setVar(self, var):
        for key in var.keys():
            exec('self.{} = {}'.format(key, var[key]))

D = {'a':1, 'b':2, 'c':3}
c = C()
c.setVar(D)

# c.a = 1
# c.b = 2
# c.c = 3

Answer 1

This is exactly what setattr is for:

def setVar(self, var):
    for key, value in var.items():
        setattr(self, key, value)

More generally, almost any time you find yourself looking at eval or exec, look for a reflective function like setattr first, and you'll almost always find one.

---

If you know your class is using a simple __dict__ for instance attributes, and all of these are instance attributes (that's the standard case—and if you don't know what all of that means, it's true for your code), you can do this quick&dirty hack:

def setVar(self, var):
    self.__dict__.update(var)

However, setattr works in any case that makes sense, and fails appropriately in most cases that doesn't, and of course it says exactly what it's doing—it's setting an attribute on self named key to value, however that attribute is stored—makes it much cleaner.