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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 buildMaskImage(rootname, bitvalue, output, extname='DQ', extver=1):
 """ Builds mask image from rootname's DQ array If there is no valid 'DQ' array in image, then return an empty string. """


    # If no bitvalue is set or rootname given, assume no mask is desired
    # However, this name would be useful as the output mask from
    # other processing, such as MultiDrizzle, so return it anyway.
    #if bitvalue == None or rootname == None:
    #    return None

    # build output name
    maskname = output

    # If an old version of the maskfile was present, remove it and rebuild it.
    if fileutil.findFile(maskname):
        fileutil.removeFile(maskname)

    # Open input file with DQ array
    fdq = fileutil.openImage(rootname, mode='readonly', memmap=False)
    try:
        _extn = fileutil.findExtname(fdq, extname, extver=extver)
        if _extn is not None:
            # Read in DQ array
            dqarr = fdq[_extn].data
        else:
            dqarr = None

        # For the case where there is no DQ array,
        # create a mask image of all ones.
        if dqarr is None:
            # We need to get the dimensions of the output DQ array
            # Since the DQ array is non-existent, look for the SCI extension
            _sci_extn = fileutil.findExtname(fdq,'SCI',extver=extver)
            if _sci_extn is not None:
                _shape = fdq[_sci_extn].data.shape
                dqarr = np.zeros(_shape,dtype=np.uint16)
            else:
                raise Exception
        # Build mask array from DQ array
        maskarr = buildMask(dqarr,bitvalue)
        #Write out the mask file as simple FITS file
        fmask = fits.open(maskname, mode='append', memmap=False)
        maskhdu = fits.PrimaryHDU(data = maskarr)
        fmask.append(maskhdu)

        #Close files
        fmask.close()
        del fmask
        fdq.close()
        del fdq

    except:
        fdq.close()
        del fdq
        # Safeguard against leaving behind an incomplete file
        if fileutil.findFile(maskname):
            os.remove(maskname)
        _errstr = "\nWarning: Problem creating MASK file for "+rootname+".\n"
        #raise IOError, _errstr
        print(_errstr)
        return None

    # Return the name of the mask image written out
    return maskname