Use the default text $EDITOR to write release notes.
        If $EDITOR is not set, use 'nano'.

def edit_release_notes():
        """Use the default text $EDITOR to write release notes.
        If $EDITOR is not set, use 'nano'."""
        from tempfile import mkstemp
        import os
        import shlex
        import subprocess

        text_editor = shlex.split(os.environ.get('EDITOR', 'nano'))

        fd, tmp = mkstemp(prefix='bumpversion-')
        try:
            os.close(fd)
            with open(tmp, 'w') as f:
                f.write(u"\n\n# Write release notes.\n"
                        u"# Lines starting with '#' will be ignored.")
            subprocess.check_call(text_editor + [tmp])
            with open(tmp, 'r') as f:
                changes = "".join(
                    l for l in f.readlines() if not l.startswith('#'))
        finally:
            os.remove(tmp)
        return changes