David C. Ullrich a écrit :
In article
<[EMAIL PROTECTED]>,
kenneth <[EMAIL PROTECTED]> wrote:
On Oct 9, 10:14 am, Christian Heimes <[EMAIL PROTECTED]> wrote:
kenneth wrote:
the 'd' variable already contains the 'self.d' value of the first
instance and not the default argument {}.
Am I doing some stupid error, or this is a problem ?
No, it always contains the default argument because default values are
created just ONE
TIME.http://effbot.org/pyfaq/why-are-default-values-shared-between-objects..
.
Wow, it's a very "dangerous" behavior ...
Just to know, is this written somewhere in the python documentation or
one has to discover it when his programs fails to work ;-) ?
At least once a week someone discovers this "problem", makes a
post about it here, and then someone points to the spot in the
documentation where it's explained.
Seems to me that people often site the "important warning" in
the tutorial. Of course there's no reason anyone would bother
going through the tutorial
Indeed. No reason at all.
- just for fun I looked in the
official Python Reference Manual to see whether they're explicit
about this or require the reader to figure it out from something
else they say.
There's a section titled "7.6 Function definitions". About halfway
through that section there's a _bold face_ statement
"Default parameter values are evaluated when the function definition is
executed.", followed by an explanation of how that can lead to
the sort of problem above.
But there's no reason to read the reference manual neither.
So I guess it _is_ awfully dangerous. They should really explain
this aspect of the language's behavior to people who don't read
the formal definition and also don't work through the tutorial.
You mean : "to people that don't bother reading the FineManual *nor*
searching the newsgroup / ML archives ?"
Well... How to say.. Is there any chance these people will read anything
*at all* ?
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