This class is actually documented in arrays.classes.rst, and it comes from numeric UserArray. It seems the idea was to allow subclassing of the numeric arrays implemented in C, the original masked arrays would be an example of such use. Grok offers an example:

from Numeric import array, Float
from UserArray import UserArray

class MyLabeledArray(UserArray):
    def __init__(self, data, label=""):
        UserArray.__init__(self, array(data, Float))
        self.label = label

    def __repr__(self):
        return f"<MyLabeledArray {self.label}: {UserArray.__repr__(self)}>"'

and offers units as another application. I suspect the motivation was difficulty inheriting from C classes.

In any case, you are correct that the resulting Python class was intended as a base class. I'm not sure it wasn't a better idea than the current masked array implementation :) Have you tested __init_subclass__?

This class is actually documented in arrays.classes.rst, and it comes from numeric UserArray. It seems the idea was to allow subclassing of the numeric arrays implemented in C, the original masked arrays would be an example of such use. Grok offers an example:

from Numeric import array, Float
from UserArray import UserArray

class MyLabeledArray(UserArray):
    def __init__(self, data, label=""):
        UserArray.__init__(self, array(data, Float))
        self.label = label

    def __repr__(self):
        return f"<MyLabeledArray {self.label}: {UserArray.__repr__(self)}>"'

and offers units as another application. I suspect the motivation was difficulty inheriting from C classes.

Ohh, that goes pretty far back then!

Have you tested __init_subclass__?

Yup:

from numpy.lib.user_array import container

class MyArray(container):
    pass

Running this demo.py with spin python demo.py (python 3.11) shows:

/home/joren/Workspace/numpy/demo.py:3: DeprecationWarning: The numpy.lib.user_array.container class is deprecated and will be removed in a future version.
  class MyArray(container):

Sounds good them. Should probably leave a note in the documentation as well, search for UserArray.

Oh, and please add a comment with the date and release, something like:

# Deprecated in NumPy 2.4, 2025-11-24

Oh, and please add a comment with the date and release, something like:

# Deprecated in NumPy 2.4, 2025-11-24

Sharp; I completely forgot about that

Thanks Joren.