How do I pass a variable by reference?

I wrote this class for testing:

class PassByReference:
    def __init__(self):
        self.variable = 'Original'
        self.change(self.variable)
        print(self.variable)

    def change(self, var):
        var = 'Changed'

When I tried creating an instance, the output was Original. So it seems like parameters in Python are passed by value. Is that correct? How can I modify the code to get the effect of pass-by-reference, so that the output is Changed?

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_{Sometimes people are surprised that code like x = 1, where x is a parameter name, doesn't impact on the caller's argument, but code like x[0] = 1 does. This happens because item assignment and slice assignment are ways to mutate an existing object, rather than reassign a variable, despite the = syntax. See Why can a function modify some arguments as perceived by the caller, but not others? for details.}

_{See also What's the difference between passing by reference vs. passing by value? for important, language-agnostic terminology discussion.}