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why?

Steve Holden sholden at holdenweb.com
Mon Dec 2 18:16:50 EST 2002 
"sami sieranoja" <sami.sieranoja at pp.inet.fi> wrote in message
news:20021203003514.2abb22e8.sami.sieranoja at pp.inet.fi...
> Hi!
>
> Why does this happen:
>
> >>> doing = ['a','b','c']
> >>> doing[1] = ('b','c')
> >>> doing[1][0]
> 'b'
> >>> doing[1][0] = 'i'
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> TypeError: object doesn't support item assignment
> >>>
>
> Why can't I change that value from 'b' to 'i' ?  Why?
>

The short answer is "you just can't". One of the fundamental properties of
any Python type is whether the values are mutable (can be changed) or
immutable (cannot be changed). Strings are immutable, and that is what the
error message is saying - that the individual characters in the string
cannot be changed.

For further enlightenment, consult the FAQ as

http://www.python.org/cgi-bin/faqw.py?query=immutable+string&querytype=allke
ywords&casefold=yes&req=search

regards
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Steve Holden                                  http://www.holdenweb.com/
Python Web Programming                 http://pydish.holdenweb.com/pwp/
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