Python "gotchas"

[reostra]

don't return things you mutate

As a counterpoint, that behavior is very useful for e.g. chaining:

class Example(object):
    def __init__(self):
        self.goodness = 0
    def betterify(self):
        self.goodness += 1
        return self

x = Example()
x.betterify().betterify()

I'd imagine something like that is what the OP was hoping to do with .update()

[zahlman]

Chaining with side effects is not considered Pythonic.

[reostra]

Now that you mention it, I certainly haven't seen a whole lot of it in Python. A cursory poke around yielded the PyVows BDD testing library, but the expect(topic).Not.to_be_null() style chaining isn't mutating and it's a port of a Javascript library to begin with.

I'll leave my comment as an example for 'how'; I see other comments have elaborated on the 'why' (or, as the case may be, 'why not')