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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def guess_timefmt(datestr):
 """ Try to guess the format a date is written in. The following formats are supported: ================= ============== =============== Format Example Python format ``YYYY-MM-DD`` 2002-04-21 %Y-%m-%d ``YYYY.MM.DD`` 2002.04.21 %Y.%m.%d ``YYYY MM DD`` 2002 04 21 %Y %m %d ``DD-MM-YYYY`` 21-04-2002 %d-%m-%Y ``DD.MM.YYYY`` 21.04.2002 %d.%m.%Y ``DD MM YYYY`` 21 04 2002 %d %m %Y ``DD/MM/YYYY`` 21/04/2002 %d/%m/%Y ================= ============== =============== These formats can also be used for seasonal (yearly recurring) time series. The year needs to be replaced by ``9999`` or another configurable year representing the seasonal year.. The following formats are recognised depending on your locale setting. There is no guarantee that this will work. ================= ============== =============== Format Example Python format ``DD-mmm-YYYY`` 21-Apr-2002 %d-%b-%Y ``DD.mmm.YYYY`` 21.Apr.2002 %d.%b.%Y ``DD mmm YYYY`` 21 Apr 2002 %d %b %Y ``mmm DD YYYY`` Apr 21 2002 %b %d %Y ``Mmmmm DD YYYY`` April 21 2002 %B %d %Y ================= ============== =============== .. note:: - The time needs to follow this definition without exception: `%H:%M:%S.%f`. A complete date and time should therefore look like this:: 2002-04-21 15:29:37.522 - Be aware that in a file with comma separated values you should not use a date format that contains commas. """


    if isinstance(datestr, float) or isinstance(datestr, int):
        return None

    seasonal_key = str(config.get('DEFAULT', 'seasonal_key', '9999'))

    #replace 'T' with space to handle ISO times.
    if datestr.find('T') > 0:
        dt_delim = 'T'
    else:
        dt_delim = ' '

    delimiters = ['-', '.', ' ', '/']
    formatstrings = [['%Y', '%m', '%d'],
                     ['%d', '%m', '%Y'],
                     ['%d', '%b', '%Y'],
                     ['XXXX', '%m', '%d'],
                     ['%d', '%m', 'XXXX'],
                     ['%d', '%b', 'XXXX'],
                     [seasonal_key, '%m', '%d'],
                     ['%d', '%m', seasonal_key],
                     ['%d', '%b', seasonal_key]]

    timeformats = ['%H:%M:%S.%f', '%H:%M:%S', '%H:%M', '%H:%M:%S.%f000Z', '%H:%M:%S.%fZ']

    # Check if a time is indicated or not
    for timefmt in timeformats:
        try:
            datetime.strptime(datestr.split(dt_delim)[-1].strip(), timefmt)
            usetime = True
            break
        except ValueError:
            usetime = False

    # Check the simple ones:
    for fmt in formatstrings:
        for delim in delimiters:
            datefmt = fmt[0] + delim + fmt[1] + delim + fmt[2]
            if usetime:
                for timefmt in timeformats:
                    complfmt = datefmt + dt_delim + timefmt
                    try:
                        datetime.strptime(datestr, complfmt)
                        return complfmt
                    except ValueError:
                        pass
            else:
                try:
                    datetime.strptime(datestr, datefmt)
                    return datefmt
                except ValueError:
                    pass

    # Check for other formats:
    custom_formats = ['%d/%m/%Y', '%b %d %Y', '%B %d %Y','%d/%m/XXXX', '%d/%m/'+seasonal_key]

    for fmt in custom_formats:
        if usetime:
            for timefmt in timeformats:
                complfmt = fmt + dt_delim + timefmt
                try:
                    datetime.strptime(datestr, complfmt)
                    return complfmt
                except ValueError:
                    pass

        else:
            try:
                datetime.strptime(datestr, fmt)
                return fmt
            except ValueError:
                pass

    return None