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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 parse(cls, fptr, offset=0, length=0):
 """Parse a codestream box. Parameters fptr : file Open file object. offset : int Start position of box in bytes. length : int Length of the box in bytes. Returns ------- ContiguousCodestreamBox Instance of the current contiguous codestream box. """

        main_header_offset = fptr.tell()
        if config.get_option('parse.full_codestream'):
            codestream = Codestream(fptr, length, header_only=False)
        else:
            codestream = None
        box = cls(codestream, main_header_offset=main_header_offset,
                  length=length, offset=offset)
        box._filename = fptr.name
        box._length = length
        return box