[Tutor] assignment statements in python

[Python]

On Sun, 2006-06-11 at 22:14 -0400, Kermit Rose wrote:
>   Message: 1
> Date: Sun, 11 Jun 2006 06:58:39 -0400
> From: Kent Johnson <kent37 at tds.net>
> Subject: Re: [Tutor] buggy bug in my program
> Cc: tutor at python.org
>  
> Assignment in Python is not a copy, it is a name binding. Assignment
> creates a name for an object. If you assign the same object to two
> names, they both are bound to the same thing. If the object is mutable,
> like a list, changes to the object will be seen regardless of which name
> you use to refer to it.
>  
> ******
>  
> I feel a little bit better now that I know that there is a reason for what
> my
> program did.
>  
> However, I still don't have any idea how to copy values from one cell in 
> an array to the adjacent cell in the same array.
>  
> I looked  at the reference ,
>  
> http://www.effbot.org/zone/python-objects.htm
>  
> that you gave,
>  
> but did not gleam any hint from it how to copy values from one place in an
> array to another place within the same array.
>  
> It must be possible, for otherwise, you could not sort an array.
>  
> 
> It is quite remarkable that my not knowing that 
>  
> assignment is not a copy 
>  
> gave me no difficulties before now.
The basic python objects: numbers, strings, and tuples are immutable and
can not be changed (mutated).
a = b = 3
b = 4	# binds b to a different object with value 4
	# the object with value 3 is unchanged
print a
3

Container objects such as lists and dictionaries can be changed in
place.
>>> a = b = [1,2,3]
>>> b.append(4) # changes (mutates) b
>>> print a
[1, 2, 3, 4]
>>> b[2] = b[3]	# positions 2 and 3 reference the same object
>>> print b
[1, 2, 4, 4]
>>> print a
[1, 2, 4, 4]


>  
> 
> 
> Kermit  <  kermit at polaris.net  >
>  
> 
> 
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Venix Corp