On Feb 21, 2:06 pm, Jeff Schwab <[EMAIL PROTECTED]> wrote:
> John Henry wrote:
> > On Feb 21, 1:48 pm, John Henry <[EMAIL PROTECTED]> wrote:
> >> On Feb 21, 1:43 pm, mrstephengross <[EMAIL PROTECTED]> wrote:
>
> >>> Hi all. In C, an assignment statement returns the value assigned. For
> >>> instance:
> >>> int x
> >>> int y = (x = 3)
> >>> In the above example, (x=3) returns 3, which is assigned to y.
> >>> In python, as far as I can tell, assignment statements don't return
> >>> anything:
> >>> y = (x = 3)
> >>> The above example generates a SyntaxError.
> >>> Is this correct? I just want to make sure I've understood the
> >>> semantics.
> >>> Thanks,
> >>> --Steve
> >> That's true, and I am happy that they decided to make that a syntax
> >> error.
>
> > BTW: The less obvious issues when coming from the C world are Python
> > syntax like these:
>
> > y = x = 3
>
> > a = 4
>
> > y = x = a
>
> > print x,y
>
> > a = 5
>
> > print x,y
>
> That's the same behavior I would expect in C, on the grounds that C
> assignments do bit-wise copies. What I found confusing at first was
> that the same variable will either directly store or merely refer to an
> object, depending on the type of the object:
>
> >>> a = [ 'hello' ]
> >>> y = x = a
> >>> a += [ 'world' ]
> >>> print x, y
> ['hello', 'world'] ['hello', 'world']
Yep. Took me a while to realize there is mutable objects, and non-
mutable objects. To be honest, I am still not too comfortable about
it. For instance, I still get nervous for code like:
def invoke_some_fct(parent):
y = parent.x
y += [ 'world' ]
print y, parent.x
class abc:
def __init__(self):
self.x=[ 'hello' ]
invoke_some_fct(self)
print self.x
hw = abc()
--
http://mail.python.org/mailman/listinfo/python-list
