Mutable strings in Python

Do you know of a Python library which provides mutable strings? Google returned surprisingly few results. The only usable library I found is http://code.google.com/p/gapbuffer/ which is in C but I would prefer it to be written in pure Python.

Edit: Thanks for the responses but I'm after an efficient library. That is, ''.join(list) might work but I was hoping for something more optimized. Also, it has to support the usual stuff regular strings do, like regex and unicode.

In Python mutable sequence type is bytearray see this link

This will allow you to efficiently change characters in a string. Although you can't change the string length.

>>> import ctypes

>>> a = 'abcdefghijklmn'
>>> mutable = ctypes.create_string_buffer(a)
>>> mutable[5:10] = ''.join( reversed(list(mutable[5:10].upper())) )
>>> a = mutable.value
>>> print `a, type(a)`
('abcdeJIHGFklmn', <type 'str'>)