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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 prepare_logfile(filename: str) -> str: """Prepare an empty log file eventually and return its absolute path. When passing the "filename" `stdout`, |prepare_logfile| does not prepare any file and just returns `stdout`: 'stdout' When passing the "filename" `default`, |prepare_logfile| generates a filename containing the actual date and time, prepares an empty file on disk, and returns its path: True For all other strings, |prepare_logfile| does not add any date or time information to the filename: True """

    if filename == 'stdout':
        return filename
    if filename == 'default':
        filename = datetime.datetime.now().strftime(
            'hydpy_%Y-%m-%d_%H-%M-%S.log')
    with open(filename, 'w'):
        pass
    return os.path.abspath(filename)