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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 frombuf(cls, buf, encoding, errors):
 """Construct a TarInfo object from a 512 byte bytes object. """

        if len(buf) == 0:
            raise EmptyHeaderError("empty header")
        if len(buf) != BLOCKSIZE:
            raise TruncatedHeaderError("truncated header")
        if buf.count(NUL) == BLOCKSIZE:
            raise EOFHeaderError("end of file header")

        chksum = nti(buf[148:156])
        if chksum not in calc_chksums(buf):
            raise InvalidHeaderError("bad checksum")

        obj = cls()
        obj.name = nts(buf[0:100], encoding, errors)
        obj.mode = nti(buf[100:108])
        obj.uid = nti(buf[108:116])
        obj.gid = nti(buf[116:124])
        obj.size = nti(buf[124:136])
        obj.mtime = nti(buf[136:148])
        obj.chksum = chksum
        obj.type = buf[156:157]
        obj.linkname = nts(buf[157:257], encoding, errors)
        obj.uname = nts(buf[265:297], encoding, errors)
        obj.gname = nts(buf[297:329], encoding, errors)
        obj.devmajor = nti(buf[329:337])
        obj.devminor = nti(buf[337:345])
        prefix = nts(buf[345:500], encoding, errors)

        # Old V7 tar format represents a directory as a regular
        # file with a trailing slash.
        if obj.type == AREGTYPE and obj.name.endswith("/"):
            obj.type = DIRTYPE

        # The old GNU sparse format occupies some of the unused
        # space in the buffer for up to 4 sparse structures.
        # Save the them for later processing in _proc_sparse().
        if obj.type == GNUTYPE_SPARSE:
            pos = 386
            structs = []
            for i in range(4):
                try:
                    offset = nti(buf[pos:pos + 12])
                    numbytes = nti(buf[pos + 12:pos + 24])
                except ValueError:
                    break
                structs.append((offset, numbytes))
                pos += 24
            isextended = bool(buf[482])
            origsize = nti(buf[483:495])
            obj._sparse_structs = (structs, isextended, origsize)

        # Remove redundant slashes from directories.
        if obj.isdir():
            obj.name = obj.name.rstrip("/")

        # Reconstruct a ustar longname.
        if prefix and obj.type not in GNU_TYPES:
            obj.name = prefix + "/" + obj.name
        return obj