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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 astype(self, dtype, copy=True):
 """Return a copy of the array after casting to a specified type. Parameters dtype : numpy.dtype or str The type of the returned array. copy : bool Default `True`. By default, astype always returns a newly allocated ndarray on the same context. If this is set to `False`, and the dtype requested is the same as the ndarray's dtype, the ndarray is returned instead of a copy. Examples -------- <type 'numpy.int32'> """

        if not copy and np.dtype(dtype) == self.dtype:
            return self

        res = zeros(shape=self.shape, ctx=self.context,
                    dtype=dtype, stype=self.stype)
        self.copyto(res)
        return res