def _w3c_date_to_pdf(string, attr_name):
    """Tranform W3C date to PDF format."""
    if string is None:
        return None
    match = W3C_DATE_RE.match(string)
    if match is None:
        LOGGER.warning(f'Invalid {attr_name} date: {string!r}')
        return None
    groups = match.groupdict()
    pdf_date = ''
    found = groups['hour']
    for key in ('second', 'minute', 'hour', 'day', 'month', 'year'):
        if groups[key]:
            found = True
            pdf_date = groups[key] + pdf_date
        elif found:
            pdf_date = f'{(key in ("day", "month")):02d}{pdf_date}'
    if groups['hour']:
        assert groups['minute']
        if groups['tz_hour']:
            assert groups['tz_hour'].startswith(('+', '-'))
            assert groups['tz_minute']
            tz_hour = int(groups['tz_hour'])
            tz_minute = int(groups['tz_minute'])
            pdf_date += f"{tz_hour:+03d}'{tz_minute:02d}"
        else:
            pdf_date += 'Z'
    return f'D:{pdf_date}'
Tranform W3C date to PDF format.
weasyprint/pdf/__init__.py