shallow copy's

[Erik Max Francis]

Rajarshi Guha wrote:

>   I have some code:
> 
> a = [1,2,3,4]
> b = a
> 
> Do some operations on a
> Will the contents of b mirror a? Or will b remain unchanged?

b will change as well, because a and b are both bound to the same object
(the list).  Note that the Subject of your message reads "shallow
copies," but this is not a copy operation at all, it is merely a
rebinding.  The way to tell if two objects are the same is with the `is'
operator; a is b will evaluate to true if a and b refer to the same
object.  This would be a shallow copy:

	import copy

	a = [1, 2, 3, 4]
	b = copy.copy(a)

or just this:

	a = [1, 2, 3, 4]
	b = a[:]

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