On 15/02/2012 18:14, Sivaram Neelakantan wrote:
I was under the impression that you have to define the attributes of
the class before using it in an instance. Following the book
'thinking in Python',
class Point:
... """pts in 2d space"""
...
print Point
__main__.Point
b = Point()
b.x =3
b.y =4
print b.y
4
Why is it not throwing an error? This is confusing me a bit.
sivaram
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Your impression is incorrect. This type of behaviour is allowed because
of Python's dynamic nature, so the following is fine.
>>> class Point:
... """pts in 2d space"""
...
>>> b = Point()
>>> b.x = 3
>>> b.y = 4
>>> del b.x
>>> del b.y
>>> b.l = 5
>>> b.m = 6
>>> print b, b.l, b.m
<__main__.Point instance at 0x02FB89B8> 5 6
Also be careful of your terminology. Here we are discussing instance
attributes. Class attributes are different in that they are are shared
at the class level so.
>>> class Point:
... """pts in 2d space"""
... x = 3
... y = 4
...
>>> a = Point()
>>> b = Point()
>>> a.x
3
>>> b.y
4
HTH.
--
Cheers.
Mark Lawrence.
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