Late-binding of function defaults (was Re: What is a function parameter =[] for?)

Thu Nov 26 01:52:07 EST 2015

Steven D'Aprano <steve at pearwood.info>:
> Making tuples mutable would break their use as dictionary keys, which is a
> *critical* use.

No, it wouldn't. Any object that provides __hash__() and __eq__() can be
used as a key.
Nothing prevents using mutable objects as keys in Python.
 Egon Spengler: There's something very important I forgot to tell you.
 Peter Venkman: What?
 Spengler: Don't use mutable keys.
 Venkman: Why?
 Spengler: It would be bad.
 Venkman: I'm fuzzy on the whole good/bad thing. What do you mean,
 "bad"?
 Spengler: Try to imagine all life as you know it stopping
 instantaneously and every molecule in your body exploding at the
 speed of light.
 Ray Stantz: Total protonic reversal!
 Venkman: Right. That's bad. Okay. All right. Important safety tip.
 Thanks, Egon.
Marko