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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 define_from_fits(cls, fitsobj, extnum=0):
 """Define class object from header information in FITS file. Parameters fitsobj: file object FITS file whose header contains the DTU information needed to initialise the members of this class. extnum : int Extension number (first extension is 0) """


        # read input FITS file
        with fits.open(fitsobj) as hdulist:
            image_header = hdulist[extnum].header
            return cls.define_from_header(image_header)