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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 decode_pdf_date(s: str) -> datetime: """Decode a pdfmark date to a Python datetime object A pdfmark date is a string in a paritcular format. See the pdfmark Reference for the specification. """

    if isinstance(s, String):
        s = str(s)
    if s.startswith('D:'):
        s = s[2:]

    # Literal Z00'00', is incorrect but found in the wild,
    # probably made by OS X Quartz -- standardize
    if s.endswith("Z00'00'"):
        s = s.replace("Z00'00'", '+0000')
    elif s.endswith('Z'):
        s = s.replace('Z', '+0000')
    s = s.replace("'", "")  # Remove apos from PDF time strings
    try:
        return datetime.strptime(s, r'%Y%m%d%H%M%S%z')
    except ValueError:
        return datetime.strptime(s, r'%Y%m%d%H%M%S')