On 01/17/2012 09:13 PM, Stayvoid wrote:
Hello!
Here is another one.
class A:
def __init__(self, data):
self.data = data
print self.data
I'm trying to understand this function-like syntax:
A('foo').__init__(42)
A(12).data
What are we actually calling this way?
Are there any other ways to get the same result?
The first line creates an instance of class A, then immediately calls
the method __init__() as though it were a normal function. It then
discards the object.
You should only call __init__() from within another class' __init__().
It's called automatically when an object is created; leave it at that.
You also usually want to keep the instance around, and use it more than
once. Otherwise you could just use ordinary functions and dispense with
the confusion.
A(12) creates an object, then you reference the data attribute of that
object, then you throw them both out. Not much use there either.
Try something like:
obj= A(49)
print obj.data
obj2 = A("artichoke")
obj.data = 99
print obj.data
print obj2.data
Two more things. Remove the print statement from methods like
__init__(), unless it's just for debugging purposes. And add a base
class of object to your class definition, so that a new-style class is
created. When you get to more advanced usage, it'll make a difference,
and you might as well use the version of class that'll still work in
Python 3.x.
class A(object):
.....
--
DaveA
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