Maxim Mercury wrote:
> here is the definintion of htmlelement
>
> class HTMLElement:
> tag=None
> attrs={}
> data=''
> childs=[]
>
> the issue is the though new elements are pushed in the stack (1),
> whenever i append the child to the stack top all other elements in the
> stack is getting affected, i assume the same reference is used but is
> there a way to overcome this ?
In
class A:
some_list = []
defines a class attribute shared by all instances of A. To turn some_list
into an instance attribute move the definition into the initializer:
class A:
def __init__(self):
self.some_list = []
Note that this holds for every attribute, but you usually see it only for
mutables like lists or dicts because in
class A:
x = "yadda"
y = []
a = A()
print a.x # yadda
a.x = 42
print a.x # 42
del a.x
print a.x # can you guess what happens?
the class attribute is shadowed by the instance attribute whereas
a.y.append(42)
modifies the class attribute in place.
# two more to check that you've understood the mechanism:
a.y += ["ham"] # ?
a.y = ["spam"] # ?
Peter
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