On 29 March 2011 08:28, Massimo Di Pierro <mdipie...@cs.depaul.edu> wrote:
> > primitive types like integers behave differently > > >>> a = 1 > >>> b = a # b and a are two different 1s > >>> b+=2 > >>> print a > 1 > > > Well, not really. Although I see what you are trying to say. numbers (like strings) are immutable. There can ever be only one number 1. You can't change a number to something else. If add 5 to 3, the number 3 doesn't change, I get a new number, 8. with "a = 1", python is still using a reference to an object. You can see this because ints have methods: >>> a = 1 >>> a.__add__ <method-wrapper '__add__' of int object at 0x009ADD38> >>> a.__add__(5) 6 >>> a 1 After a 'b = a' statement, b and a point to the same object (in this case, the one at 0x009ADD38): >>> b = a >>> b.__add__ <method-wrapper '__add__' of int object at 0x009ADD38> >>> Remember, the object that both b and a reference is immutable. It's the number 1. You can't change the number one to be some other number. If you then do 'b += 2', python calculates the result of the expression 'b + 2', which is 3, and then changes b's reference to point to the object representing the int 3. Cheers, Carl.
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