I'm currently migrating all existing (incomplete) documentation to Sphinx.

The problem is that the documentation uses Python docstrings (the module is written in C, but it probably does not matter) and the class documentation must be converted into a form usable for Sphinx.

There is sphinx.ext.autodoc, but it automatically puts current docstrings to the document. I want to generate a source file in (RST) based on current docstrings, which I could then edit and improve manually.

How would you transform docstrings into RST for Sphinx?

The autodoc does generate RST only there is no official way to get it out of it. The easiest hack to get it was by changing sphinx.ext.autodoc.Documenter.add_line method to emit me the line it gets.

As all I want is one time migration, output to stdout is good enough for me:

def add_line(self, line, source, *lineno):"""Append one line of generated reST to the output."""print(self.indent + line)self.directive.result.append(self.indent + line, source, *lineno)

Now autodoc prints generated RST on stdout while running and you can simply redirect or copy it elsewhere.