Inheriting dictionary attributes and manipulate them in subclasses
Hi,
I just stumbled upon the following behaviour.
class base():
... dic = {'1':'1', '2':'2'}
...
class child1(base):
... def __init__(self):
... self.dic.update({'1':'2'})
...
class child2(base):
... pass
...
c1 = child1()
c2 = child2()
print c1.dic
{'1': '2', '2': '2'}
print c2.dic
{'1': '2', '2': '2'}
This is not what I have excepted.
Although I know the solution to get what I want...
class base():
... def __init__(self):
... self.dic = {'1':'1', '2':'2'}
...
class child1(base):
... def __init__(self):
... base.__init__(self)
... self.dic.update({'1':'2'})
...
class child2(base):
... pass
...
c1 = child1()
c2 = child2()
print c1.dic
{'1': '2', '2': '2'}
print c2.dic
{'1': '1', '2': '2'}
... I wonder if there is a special reason for the behaviour in the
first example.
Shouldn't the first example behave like the second?
cheers
Dominik
--
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Re: Inheriting dictionary attributes and manipulate them in subclasses
Dominik Ruf wrote:
Hi,
I just stumbled upon the following behaviour.
class base():
... dic = {'1':'1', '2':'2'}
...
class child1(base):
... def __init__(self):
... self.dic.update({'1':'2'})
...
class child2(base):
... pass
...
c1 = child1()
c2 = child2()
print c1.dic
{'1': '2', '2': '2'}
print c2.dic
{'1': '2', '2': '2'}
This is not what I have excepted.
Although I know the solution to get what I want...
class base():
... def __init__(self):
... self.dic = {'1':'1', '2':'2'}
...
class child1(base):
... def __init__(self):
... base.__init__(self)
... self.dic.update({'1':'2'})
...
class child2(base):
... pass
...
c1 = child1()
c2 = child2()
print c1.dic
{'1': '2', '2': '2'}
print c2.dic
{'1': '1', '2': '2'}
... I wonder if there is a special reason for the behaviour in the
first example.
Shouldn't the first example behave like the second?
No, because you are creating *classvariables* when declaring things like
this:
class Foo(object):
bar = {}
If these are mutable, changing them will change them for *all* instances.
OTOH, when assigning to an instance, this will create an
*instance*-variable. Which is what
self.some_name = some_value
does.
Diez
--
http://mail.python.org/mailman/listinfo/python-list
Variables vs attributes [was Re: Inheriting dictionary attributes and manipulate them in subclasses]
On Fri, 17 Apr 2009 17:48:55 +0200, Diez B. Roggisch wrote: No, because you are creating *classvariables* when declaring things like this: ... OTOH, when assigning to an instance, this will create an *instance*-variable. Which is what If an integer variable is an integer, and a string variable is a string, and float variable is a float, and a list variable is a list (there's a pattern here), shouldn't a class variable be a class and an instance variable be an instance? I had never noticed the usage of variable to mean attribute until a few months ago. What's going on? Why did people decide that confusing variables and attributes of variables was a good thing? What's next, describing dictionary keys as dictionary variables? Sorry to pick on Diez, he's not the only one, just the latest example. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
