staticmethod behaviour
Hi, I run today into some problems with my code and I realized that there is something in the behaviours of the @staticmethod that I don't really understand. I don't know if it is an error or not, actually, only that it was, definitely, unexpected. I wrote a small demo of what happens. The code: http://dpaste.com/hold/233795/ The answer I get: User created with static: id, rights, rights2 1 ['read', 'write'] ['write2'] ['write3'] User created with User() None [] ['write2'] ['write3'] I was expecting either all arrays from the second to be [] or to be a copy of the first one. If someone can provide an explanation, I would be thankful :) Regards, Samu -- http://mail.python.org/mailman/listinfo/python-list
Re: staticmethod behaviour
On Aug 25, 3:03 pm, Samu wrote:
> Hi,
>
> I run today into some problems with my code and I realized that there
> is something in the behaviours of the @staticmethod that I don't
> really understand. I don't know if it is an error or not, actually,
> only that it was, definitely, unexpected.
>
> I wrote a small demo of what happens.
>
> The code:http://dpaste.com/hold/233795/
>
> The answer I get:
> User created with static: id, rights, rights2
> 1 ['read', 'write'] ['write2'] ['write3']
> User created with User()
> None [] ['write2'] ['write3']
>
> I was expecting either all arrays from the second to be [] or to be a
> copy of the first one.
>
> If someone can provide an explanation, I would be thankful :)
>
> Regards,
> Samu
In addition, if I don't define the function as static, but either as a
method of the object or a function outside of the class, something
like this:
def cr_user():
user = User(1, ['read'], rights3=[])
user.rights.append('write')
user.rights2.append('write2')
user.rights3.append('write3')
return user
I get instead:
User created with static: id, rights, rights2
1 ['read', 'write'] ['write2'] ['write3']
User created with User()
None [] ['write2'] []
There is some (maybe deep) concept that I don't get it seems, because
that output puzzles me...
--
http://mail.python.org/mailman/listinfo/python-list
Re: staticmethod behaviour
On Aug 25, 3:26 pm, Peter Otten <[email protected]> wrote: > Samu wrote: > > Hi, > > > I run today into some problems with my code and I realized that there > > is something in the behaviours of the @staticmethod that I don't > > really understand. I don't know if it is an error or not, actually, > > only that it was, definitely, unexpected. > > > I wrote a small demo of what happens. > > The code: > > class User: > > def __init__(self, id=None, rights=[], rights2=[], rights3=[]): > > self.id = id > > self.rights = rights > > self.rights2 = rights2 > > self.rights3 = rights3 > > �...@staticmethod > > def cr_user(): > > user = User(1, ['read'], rights3=[]) > > user.rights.append('write') > > user.rights2.append('write2') > > user.rights3.append('write3') > > return user > > > print "User created with static: id, rights, rights2" > > a = User.cr_user() > > print a.id, a.rights, a.rights2, a.rights3 > > print "User created with User()" > > b = User() > > print b.id, b.rights, b.rights2, a.rights3 > > The answer I get: > > User created with static: id, rights, rights2 > > 1 ['read', 'write'] ['write2'] ['write3'] > > User created with User() > > None [] ['write2'] ['write3'] > > > I was expecting either all arrays from the second to be [] or to be a > > copy of the first one. > > > If someone can provide an explanation, I would be thankful :) > > The problem is not the staticmethod, it's the mutable default values for > __init__(). See > > http://effbot.org/zone/default-values.htm > > Peter Ahh, thank you very much for the link. Now I understand. I remember having read that before, but it is not until you face the problem that the concept sticks. But why does it have a different behaviour the staticmethod with the "rights3" case then? -- http://mail.python.org/mailman/listinfo/python-list
Re: staticmethod behaviour
On Aug 25, 4:32 pm, Peter Otten <[email protected]> wrote: > Samu wrote: > > the concept sticks. But why does it have a different behaviour the > > staticmethod with the "rights3" case then? > > Moving from staticmethod to standalone function doesn't affect the output. > You have inadvertently changed something else. > > Peter Absolutely right. Thank you very much for your time and answers, Peter :) It helped me a lot! -- http://mail.python.org/mailman/listinfo/python-list
