Is it always safe to pass empty dict as keywords argument?

Question

Are there any cases where

f(arg1, arg2..., argN)

works and produces a result and

f(arg1, arg2..., argN, **{} )

yields a different result, or causes an error?

I'm assuming that a **kwds doesn't already occur in the argument list.

The context is that I'm writing a functor that holds a function and it's arguments for later evaluation, and want to support optional keywords.

score 3 · Accepted Answer · answered Jul 26 '12 at 19:58

3

Yes, this is always safe to do. The two calls are completely equivalent, and the function f() has no way to distinguish them (except for introspecting the source code, of course).

answered Jul 26 '12 at 19:58

Sven Marnach

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Does the mutability of a `dict` not matter here? – inspectorG4dget Jul 26 '12 at 20:05
1

@inspectorG4dget: No, it will be copied before being passed in. – Sven Marnach Jul 26 '12 at 20:07
Thanks, I thought maybe something weird could happen if `f` were implemented in c – Dave Jul 26 '12 at 20:34
@Dave: No, not even then. Internally, the function will get passed an empty dictionary of keyword arguments in *both* cases. – Sven Marnach Jul 26 '12 at 20:42

Is it always safe to pass empty dict as keywords argument?

1 Answers1