Is Python string immutable?

[Frank Potter]

Thank you very much.
Steve Holden, I post my soucecode at my blog here:
http://hiparrot.wordpress.com/2005/12/08/implementing-a-simple-net-spider/
I wish you can read and give me some suggestion.
Any comments will be appreciated.

On 12/2/05, Steve Holden <steve at holdenweb.com> wrote:
>
> could ildg wrote:
> > In java and C# String is immutable, str=str+"some more" will return a
> > new string and leave some gargabe.
> > so in java and C# if there are some frequent string operation,
> > StringBuilder/StringBuffer is recommanded.
> >
> > Will string operation in python also leave some garbage? I implemented a
> > net-spider in python which includes many html string procession. After
> > it running for sometime, the python exe eats up over 300M memory. Is
> > this because the string garbages?
> >
> If you create garbage in a Python program it will normally be collected
> and returned to free memory by the garbage collector, which should be
> run when memory is exhausted in preference to allocating more memory.
> Additional memory should therefore only be claimed when garbage
> collection fails to return sufficient free space.
>
> If cyclic data structures are created (structures in which components
> refer to each other even though no external references exist) this could
> cause problems in older versions of Python, but nowadays the garbage
> collector also takes pains to collect unreferenced cyclic structures.
>
> > If String in python is immutable, what class should I use to avoid too
> > much garbages when processing strings frequently?
> >
> The fact that your process uses 300MB implies that you are retaining
> references to a large amount of data. Without seeing the code, however,
> it's difficult to suggest how you might improve the situation. Are you,
> for example, holding the HTML for every spidered page?
>
> As a side note, both C# and Java also use garbage collection, so if your
> algorithm exhibits the same problem in all three languages this merely
> confirms that the problem really is your algorithm, and not the language
> in which it is implemented.
>
> regards
>   Steve
> --
> Steve Holden       +44 150 684 7255  +1 800 494 3119
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>
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