How to write a quickfix list to a file

I'm looking for a way to write content of a quickfix window to a file with a specific formatting, preferably in a way that is easily scriptable.

What I'm trying to achieve is a very light integration of Vim and ipdb:

1. I set 'breakpoints' as items on a quickfix list with mapping: nmap <leader>s :call setqflist([], 'a', {'items': [{'filename': @%, 'lnum':line('.'), 'text':'break'}]})
2. Write content of the quickfix to .pdbrc file with break file_path:line_number formatting
3. Run ipdb on specified script

You have two problems:

1. Turning items into a list of properly formatted lines.

   You will need to:

   • get the quickfix list with :help getqflist(),
   • format each item of the list with :help map(),
   • derive file_path from the bufnr field with :help bufname() and possibly :help fnamemodify().

2. Writing that list to a given file.

   You will need :help writefile().