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

Guido van Rossum guido at python.org
Fri Apr 16 23:31:25 CEST 2010

On Fri, Apr 16, 2010 at 2:22 PM, Maciej Fijalkowski <fijall at gmail.com> wrote:

On Fri, Apr 16, 2010 at 3:11 PM, Raymond Hettinger <raymond.hettinger at gmail.com> wrote:

Guido van Rossum, 16.04.2010 16:33:

I am fine with declaring dict({}, **{1:3}) illegal, since after all it is abuse of the ** mechanism. ISTM that making it illegal costs cycles with giving any real benefit. It is reasonably common to accept **kwds and then pass it down to another function.  Do we want to validate the keys of every kwds dict on every call?  Why do we even care? If I'm understanding the proposal correctly, it means that every existing application using **kwds will pay a price, either by breaking (because it uses non-string keys) or by running slower (so that every call can be checked to make sure it didn't use string keys). Raymond On the other hand, we (as in alternative python implementations) are paying the price because people use it, even if only accidentally. If CPython detects such cases and complain early, it would be much easier for applications to stay cross-interpreter compatible (and I don't think it's a huge burden for them to get rid of that, django already did).

+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.

-- --Guido van Rossum (python.org/~guido)

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