[Python-mode] code/macros to reformat code

[m h]

Folks-

I was wondering if anyone has some code floating around to reformat
code after the code passes a certain column (say 79 or 80).

What I'm looking for is reformatting long lines. I'd like to convert
something like (assume the k of junk is around 78):

my_string = "foo bar baz ... junk stuff etc"

to:

my_string = "foo bar baz ... junk"
                     "stuff etc"

My searches have turned up nothing, but I'm assuming someone has something.

cheers,
-matt