ENH: Ensure that repr and str work for MaskedArray non-ndarray bases - #4576

import numpy as np

class ComplicatedSubArray(np.ndarray):
    def __new__(cls, arr):
        return np.asanyarray(arr).view(cls)

    def __str__(self):
        return 'myprefix {0} mypostfix'.format(
            super(ComplicatedSubArray, self).__str__())

    def __repr__(self):
        # Return a repr that does not start with 'name('
        return '<{0} {1}>'.format(self.__class__.__name__, self)

    def __setitem__(self, item, value):
        # this ensures direct assignment to masked_print_option will fail
        if not isinstance(value, ComplicatedSubArray):
            raise ValueError("Can only set to MySubArray values")
        super(ComplicatedSubArray, self).__setitem__(item, value)

xcsub = ComplicatedSubArray(np.arange(5))
mxcsub1 = np.ma.masked_array(xcsub)
mxcsub2 = np.ma.masked_array(xcsub, mask=[True, False, True, False, False])

In [15]: mxcsub1
Out[15]: 
masked_<ComplicatedSubArray myprefix [0 1 2 3 4] mypostfix>(data = myprefix [0 1 2 3 4] mypostfix,
                                                            mask = False,
                                                      fill_value = 999999)
In [16]: mxcsub2
Out[16]: 
.
.
.
ValueError: Can only set to MySubArray values

In [2]: mxcsub1
Out[2]: 
masked_ComplicatedSubArray(data = myprefix [0 1 2 3 4] mypostfix,
                           mask = False,
                     fill_value = 999999)
In [3]: mxcsub2
Out[3]: 
masked_ComplicatedSubArray(data = myprefix [-- 1 -- 3 4] mypostfix,
                           mask = [ True False  True False False],
                     fill_value = 999999)