confused about Python assignment

[Emile van Sebille]

"Haoyu Zhang" <flyfeather at myrealbox.com> wrote in message
news:d5a952e4.0310301749.3126b961 at posting.google.com...
> Dear Friends,
> Python assignment is a reference assignment. However, I really can't
> explain the difference in the following example. When the object is
> a list, the assignment seems to be a reference. However, when the
> object is a number, the story is so different. I don't understantd
> for what reason Python deals with them differently. The example is
> as follows:
>
> >>> a = [3, 2,1]

bind the label 'a' to the mutable list [3,2,1]

> >>> b = a

bind 'b' to what 'a' is bound to

> >>> a,b
> ([3, 2, 1], [3, 2, 1])
> >>> a[1]=0

replace index 1 in what 'a' is bound to with '0'

> >>> a,b
> ([3, 0, 1], [3, 0, 1])
> >>> c = 1

bind c to the immutable integer 1

> >>> d = c

bind 'd' to what 'c' is bound to

> >>> c,d
> (1, 1)
> >>> c=0

now bind c to the immutable integer 0

> >>> c,d
> (0, 1)


HTH,

Emile van Sebille
emile at fenx.com