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# Extensions

These are primarily intended for library authors looking to extend pandas objects.

`api.extensions.register_extension_dtype`(cls) | Register an ExtensionType with pandas as class decorator.
`api.extensions.register_dataframe_accessor`(name) | Register a custom accessor on DataFrame objects.
`api.extensions.register_series_accessor`(name) | Register a custom accessor on Series objects.
`api.extensions.register_index_accessor`(name) | Register a custom accessor on Index objects.

`api.extensions.ExtensionDtype`() | A custom data type, to be paired with an ExtensionArray.
`api.extensions.ExtensionArray`() | Abstract base class for custom 1-D array types.
`arrays.NumpyExtensionArray`(values[, copy]) | A pandas ExtensionArray for NumPy data.

Additionally, we have some utility methods for ensuring your object behaves correctly.

`api.indexers.check_array_indexer`(array, indexer) | Check if indexer is a valid array indexer for array.

The sentinel `pandas.api.extensions.no_default` is used as the default value in some methods. Use an `is` comparison to check if the user provides a non-default value.