Naive idiom questions

* Why are there no real mutable strings available?

I found MutableString in UserString, but further research indicates
that it is horribly inefficient and actually just wraps immutable
strings for the implementation.

I want to be able to accumulate a string with +=, not by going
through an intermediate list and then doing ''.join(), because I
think the latter is ugly. There are also times when I'd like to use
the string as a modifiable buffer.

Is the python idiom that this is actually the Right Thing for
reasons I'm not seeing? Is there a fundamental reason it would be
hard to implement a mutable string in cpython?

* What's the best way to initialize a list of lists?

I keep wanting to do this:

l=[[None]*5]*5

as do many other Python novices, but of course it quickly becomes
apparent why this is a bad idea as soon as one modifies a value.
The best I've found is:

l=[[None]*5 for i in range(5)]

I don't particularly like it, though. It bothers me to have to
explain list comprehensions, which are a moderately advanced feature
conceptually, just to initialize an array. We could get around this
if we had a defaultlist, but we don't. Is there a more elegant
solution here?

* Is there a way to get headings in docstrings?

I want to create my own sections, like "OVERVIEW", "EXAMPLES",
"AUTHORS", "BUGS", etc. I can't figure out any way to do this. In
perldoc, I can easily use =head1, but I can't figure out the Python
equivalent. At first I thought I could use (re)structuredtext, but
then it became apparent that pydoc(1) does not parse any of this
markup. Am I missing something, or is it just not possible to
achieve this effect other than by writing separate, independent
manpages?

Thanks for any suggestions or thoughts.
.

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