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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 getflat(self, chip):
 """ Method for retrieving a detector's flat field. Returns ------- flat: array This method will return an array the same shape as the image in **units of electrons**. """

        sci_chip = self._image[self.scienceExt, chip]
        # The keyword for ACS flat fields in the primary header of the flt
        # file is pfltfile.  This flat file is already in the required
        # units of electrons.

        # The use of fileutil.osfn interprets any environment variable, such as
        # jref$, used in the specification of the reference filename
        filename = fileutil.osfn(self._image["PRIMARY"].header[self.flatkey])
        hdulist = None
        try:
            hdulist = fileutil.openImage(filename, mode='readonly',
                                         memmap=False)
            data = hdulist[(self.scienceExt, chip)].data

            if data.shape[0] != sci_chip.image_shape[0]:
                ltv2 = int(np.round(sci_chip.ltv2))
            else:
                ltv2 = 0
            size2 = sci_chip.image_shape[0] + ltv2

            if data.shape[1] != sci_chip.image_shape[1]:
                ltv1 = int(np.round(sci_chip.ltv1))
            else:
                ltv1 = 0
            size1 = sci_chip.image_shape[1] + ltv1

            flat = data[ltv2:size2, ltv1:size1]

        except FileNotFoundError:
            flat = np.ones(sci_chip.image_shape, dtype=sci_chip.image_dtype)
            log.warning("Cannot find flat field file '{}'".format(filename))
            log.warning("Treating flatfield as a constant value of '1'.")

        finally:
            if hdulist is not None:
                hdulist.close()

        return flat