[Tutor] 2D list assignment

[Gregor Lingl]

Shitiz Bansal schrieb:

> Hi,
> This is a sample python code:
> a=((2,4),(4,2))
>
>
> a[1][1]=4
> Traceback (most recent call last):
> File "<pyshell#2>", line 1, in -toplevel-
> a[1][1]=4
> TypeError: object doesn't support item assignment
> Is it a bug or am i missing the point?

It's not a bug!

You create a data structure and then try to change it (i.e. it'S content).

In Python there are several types of "sequences", among them:

tuples, which are immutable and
lists which are mutable.

You used a tuple (of tuples), designated by parentheses ()
Instead you should have used lists, designated by brackets [],
because only they are mutable:
 >>> a=[[2,4],[4,2]]
 >>> a[1][1]=4
 >>> a
[[2, 4], [4, 4]]

See Docs: Python Library reference, 2.3.6 Sequence Types
and especially 2.3.6.4 Mutable Sequence Types

Regards,
Gregor


> Shitiz
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