problem manipulating a list belonging to a class

[Marc Leconte]

Dear all,

I have a problem with the following code (ubuntu 8.04, Python 2.5.2):

class Toto(object):
def __init__(self, number, mylist=[]):
self.number=number
self.mylist=mylist
pass
pass

listA=Toto(number=1)
listB=Toto(number=2)

listA.mylist.append(5)
print "1) ", listA.mylist
print "2) ", listB.mylist

1) [5]
2) [5]

I would have expected

1) [5]
2) []

Thanks in advance for advice,
Marc.

 

[Diez B. Roggisch]

Dear all,

I have a problem with the following code (ubuntu 8.04, Python 2.5.2):

class Toto(object):
def __init__(self, number, mylist=[]):
self.number=number
self.mylist=mylist
pass
pass

listA=Toto(number=1)
listB=Toto(number=2)

listA.mylist.append(5)
print "1) ", listA.mylist
print "2) ", listB.mylist

1) [5]
2) [5]

I would have expected

1) [5]
2) []

http://effbot.org/zone/default-values.htm

Diez

 

[Steve Howell]

Dear all,

I have a problem with the following code (ubuntu 8.04, Python 2.5.2):

class Toto(object):
        def __init__(self, number, mylist=[])
                self.number=number
                self.mylist=mylist
                pass
        pass

Change your code to do this:

def __init__(self, number, mylist=None):
if mylist is None:
self.mylist = []
else:
self.mylist = mylist

Explanations of why you need to write it that will follow...

 

[Steve Howell]

Explanations of why you need to write it that will follow...

I knew this had to be written up somewhere...

http://www.ferg.org/projects/python_gotchas.html#contents_item_6

 

[Lie Ryan]

class Toto(object):
def __init__(self, number, mylist=[]):
self.number=number
self.mylist=mylist
pass
pass

Why are you using pass to end your blocks?

 

[Marc Leconte]

Thx all, good to know

Le dimanche 22 novembre 2009 à 15:16 -0800, Steve Howell a écrit :