On 4/25/2011 4:59 AM, Colin J. Williams wrote:
On 24-Apr-11 13:07 PM, Ken Seehart wrote:
On 4/24/2011 2:58 AM, Steven D'Aprano wrote:
Consider this in Python 3.1:
def f(a=42):
... return a
...
f()
42
f.__defaults__ = (23,)
f()
23
Is this an accident of implementation, or can I trust that changing
function defaults in this fashion is guaranteed to work?
This is documented in python 3, so I would expect it to be stable (until
python 4, that is)
http://docs.python.org/py3k/whatsnew/3.0.html#operators-and-special-methods
http://docs.python.org/py3k/library/inspect.html#types-and-members
The f.__defaults__ attribute was previously known as f.func_defaults (in
python 2.x), which has been around, documented and stable for quite a
while.
So it's probably just as safe as any other monkey patching technique. :)
Best of luck,
Ken
Wouldn't it make more sense to return a dictionary instead of a tuple?
Colin W.
I assume you mean making the value of f.__defaults__ a dictionary
instead of a tuple.
A dictionary would be slower to process since it would have to iterate
the dictionary keys and assign arguments by name.
Since argument defaults can only be applied to the rightmost contiguous
sequence of zero or more parameters (excluding *args,**kwargs), a tuple
is sufficient to cover all cases, so a dictionary would provide no
advantage.
Also, a dictionary would produce an unnecessary error case (if a key in
the dictionary is not the name of an argument).
Good question though.
Cheers,
Ken
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