<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def update_project_files(cfg, proj_version):
 """ Update version string in project files :rtype : dict :param cfg:project configuration :param proj_version:current version :return:dict :raise ValueError: """

    counters = {'files': 0, 'changes': 0}

    for project_file in cfg.files:
        if not project_file.file.exists():
            print("File \"%s\" not found" % project_file.filename, file=sys.stderr)
            continue

        # prepare data
        date_format = project_file.date_format or cfg.date_format

        rxp = re.compile(project_file.search, project_file.search_flags)
        replace = project_file.replace % {
            "date": time.strftime(date_format),
            "major": proj_version.major,
            "minor": proj_version.minor,
            "patch": proj_version.patch,
            "prerelease": proj_version.prerelease,
            "version": str(proj_version),
            "build": proj_version.build,
        }

        # update project files
        with \
                project_file.file.open(mode="r", encoding=project_file.encoding) as fh_in, \
                tempfile.NamedTemporaryFile(mode="w", encoding=project_file.encoding, delete=False) as fh_out:
            if project_file.match == 'line':
                changes = 0
                for line in fh_in:
                    (line, cnt) = rxp.subn(replace, line)
                    if cnt:
                        changes += cnt
                    fh_out.write(line)

                if changes:
                    counters['files'] += 1
                    counters['changes'] += changes

            elif project_file.match == 'file':
                data = fh_in.read()
                (data, cnt) = rxp.subn(replace, data)
                if cnt:
                    counters['files'] += 1
                    counters['changes'] += cnt
                fh_out.write(data)

            else:
                raise ConfigError("Unknown match type: \"%s\"" % project_file.match)

            fh_out.close()

            shutil.copystat(project_file.filename, fh_out.name)
            pathlib.Path(fh_out.name).rename(project_file.filename)

    return counters