ADD_LAZYFUNCS.md

Adding (lazy) functions

Once you have written a (public API) function in Blosc2, it is important to:

• Import it from the relevant module in the __init__.py file
• Add it to the list of functions in __all__ in the __init__.py file
• If it is present in numpy, add it to the relevant dictionary (local_ufunc_map, ufunc_map ufunc_map_1param) in ndarray.py

If your function is implemented at the Blosc2 level (and not via either the LazyUDF or LazyExpr classes), you will need to add some conversion of the inputs to SimpleProxy instances (see e.g. matmul for an example).

Finally, you also need to deal with it correctly within shape_utils.py.

If the function does not change the shape of the output, simply add it to elementwise_funcs and you're done.

If the function does change the shape of the output, it is likely either a reduction, a constructor, or a linear algebra function and so should be added to one of those lists (reducers, constructors or linalg_funcs). If the function is a reduction, unless you need to handle an argument that is neither axis nor keepdims, you don't need to do anything else. If your function is a constructor, you need to ensure it is handled within the visit_Call function appropriately (if it has a shape argument this is easy, just add it to the list of functions that have zeros, zeros_like etc.).

For linear algebra functions, you will likely have to write a bespoke shape handler within the linalg_shape function. There is also a list linalg_attrs for attributes which change the shape (currently only T and mT) should you need to add one. You will probably need to edit the validation_patterns list at the top of the lazyexpr.py file to handle these attributes. Just extend the part that has the negative lookahead "(?!real|imag|T|mT|(".

After this, the imports at the top of the lazyexpr.py should handle things, where an eager_funcs list is defined to handle eager execution of functions which change the output shape. Finally, in order to handle name changes between NumPy versions 1 and 2, it may be necessary to add aliases for functions within the blocks defined by if NUMPY_GE_2_0: in lazyexpr.py and ndarray.py.