[Python-Dev] Very Strange Argument Handling Behavior (original) (raw)

Xavier Morel python-dev at masklinn.net
Sat Apr 17 12:53:34 CEST 2010

On 16 Apr 2010, at 23:31 , Guido van Rossum wrote:

+1. Apparently dict(x, **y) is going around as "cool hack" for "call x.update(y) and return x". Personally I find it more despicable than cool.

This description doesn't make sense since dict(x, **y) returns not an updated x but a new dictionary merging x and y.

And that's how (and why) I use it, it's simpler (and — I believe — more readable) to write z = dict(x, **y) than z = dict(x); z.update(y), since Python doesn't overload addition as it does for lists: l3 = l1 + l2 works and is equivalent to l3 = list(l1); l3.extend(l2)

but there is no easy way to say that with dicts, at the moment.

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