Hi, I have just encountered a Python behaviour I wouldn't expect. Take
the following code:
------------------------------------------------------------------------
class Parent:
a = 1
def m (self, param = a):
print "param = %d" % param
class Child (Parent):
a = 2
p = Parent ()
p.m ()
c = Child ()
c.m ()
------------------------------------------------------------------------
I would expect to receive the following output:
param = 1
param = 2
But actually I get:
param = 1
param = 1
Is this the correct behaviour, and then why, or is it a bug? For
reference, I am using Python 2.5.1 on UNIX.
Thanks in advance!
5  939 
sukkop...@gmail .com napisa³(a):
Hi, I have just encountered a Python behaviour I wouldn't expect. Take
the following code:
------------------------------------------------------------------------
class Parent:
a = 1
def m (self, param = a):
print "param = %d" % param
class Child (Parent):
a = 2
p = Parent ()
p.m ()
c = Child ()
c.m ()
------------------------------------------------------------------------
I would expect to receive the following output:
param = 1
param = 2
But actually I get:
param = 1
param = 1
Is this the correct behaviour, and then why, or is it a bug? For
reference, I am using Python 2.5.1 on UNIX.
Thanks in advance!
I expect it's because default values for parameters are evaluated and
bound at definition time. So once "def m (self, param = a):" line
executes, the default value for parameter is forever bound to be 1.
What you can do is for example:
def m (self, param = None):
if param is None: param = self.a
print "param = %d" % param
Regards,
Marek
On 13 Lug, 19:42, marek.ro...@wp. pl wrote:
I expect it's because default values for parameters are evaluated and
bound at definition time. So once "def m (self, param = a):" line
executes, the default value for parameter is forever bound to be 1.
What you can do is for example:
Yes, that's what I thought, too. Although, it does not seem to me the
correct thing that has to be done, that is why I reported it.
Also thanks for your suggestion, that might work, even though I
already have implemented a workaround (two different methods).
Regards! su*******@gmail .com <su*******@gmai l.com>:
On 13 Lug, 19:42, marek.ro...@wp. pl wrote:
>I expect it's because default values for parameters are evaluated and
bound at definition time. So once "def m (self, param = a):" line
executes, the default value for parameter is forever bound to be 1.
What you can do is for example:
Yes, that's what I thought, too. Although, it does not seem to me the
correct thing that has to be done, that is why I reported it.
It _is_ the correct thing. Evaluation of default parameters at "declaratio n
time" and not at invocation is truely a language feature, not a bug.
You'll find your bug report being closed quickly.
--
Freedom is always the freedom of dissenters.
(Rosa Luxemburg)
On 18 Lug, 13:23, "Sebastian \"lunar\" Wiesner"
<basti.wies...@ gmx.netwrote:
It _is_ the correct thing. *Evaluation of default parameters at "declaratio n
time" and not at invocation is truely a language feature, not a bug.
You'll find your bug report being closed quickly.
It has ;). I had totally missed the tutorial section where it is
stated, which actually even has an example quite close to the one I
provided. Sorry for the waste of time.
Giorgio This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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