How to use the unidiff.constants.RE_SOURCE_FILENAME.match function in unidiff

if current_file is not None:
                    raise UnidiffParseError('Target without source: %s' % line)
                # prefix with 'b/' to match expected git source format
                target_file = (
                    'b/' + is_rename_target_filename.group('filename'))
                # keep line as patch_info
                patch_info.append(line)
                # add current file to PatchSet
                current_file = PatchedFile(
                    patch_info, source_file, target_file, None, None,
                    is_rename=True)
                self.append(current_file)
                continue

            # check for source file header
            is_source_filename = RE_SOURCE_FILENAME.match(line)
            if is_source_filename:
                source_file = is_source_filename.group('filename')
                source_timestamp = is_source_filename.group('timestamp')
                # reset current file, unless we are processing a rename
                # (in that case, source files should match)
                if current_file is not None and not (current_file.is_rename and
                        current_file.source_file == source_file):
                    current_file = None
                continue

            # check for target file header
            is_target_filename = RE_TARGET_FILENAME.match(line)
            if is_target_filename:
                if current_file is not None and not current_file.is_rename:
                    raise UnidiffParseError('Target without source: %s' % line)
                target_file = is_target_filename.group('filename')

def parse_unidiff(diff):
    """Unified diff parser, takes a file-like object as argument."""
    ret = PatchSet()
    current_patch = None

    for line in diff:
        # check for source file header
        check_source = RE_SOURCE_FILENAME.match(line)
        if check_source:
            source_file = check_source.group('filename')
            source_timestamp = check_source.group('timestamp')
            current_patch = None
            continue

        # check for target file header
        check_target = RE_TARGET_FILENAME.match(line)
        if check_target:
            target_file = check_target.group('filename')
            target_timestamp = check_target.group('timestamp')
            current_patch = PatchedFile(source_file, target_file,
                                        source_timestamp, target_timestamp)
            ret.append(current_patch)
            continue