numpy.ma.MaskedArray.harden_mask
method
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MaskedArray.harden_mask()[source]
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Force the mask to hard. Whether the mask of a masked array is hard or soft is determined by its hardmaskproperty.harden_masksetshardmaskto True.See also 
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Licensed under the 3-clause BSD License.
    https://docs.scipy.org/doc/numpy-1.16.1/reference/generated/numpy.ma.MaskedArray.harden_mask.html