[Tutor] string immutability

[Andreas Perstinger]

On 2011-10-24 20:04, Johan Martinez wrote:
> Hi,
>
> I am struggling to understand Python string immutability. I am able to
> modify Python string object after initializing/assigning it a value.
>
>>>>  s = "First"
>>>>  print s.__class__
> <type 'str'>
>>>>  print s
> First
>>>>  s = "Second"
>>>>  print s
> Second

Dave, Sander and Wayne have already explained why you aren't modifying 
string objects in your example.
With the id()-function you can also see what is happening:

 >>> s = "First"
 >>> id(s)
3077110080L    # In CPython this is the memory address of the object
                # with the name 's' (in your case "First")
 >>> s = "Second"
 >>> id(s)
3077110304L    # You see that 's' refers now to another address
 >>> id("First")
3077110080L    # But "First" is still on the same address as before
 >>> id("Second")
3077110304L    # And this proves that "Second" is at the address
                # which 's' refers to

Bye, Andreas