API Reference - Extensions

This section provides more details on the extension files and how to define the patches in there.

This module contains the utilities to extend WSMOD with new features.

The register_node_patch decorator is used to register a function that will be used instead of a method or attribute of a node. The apply_patches function applies all registered patches to a model.

Example of patching a method:

empty_distributed will be called instead of pull_distributed of "my_node":

>>> from wsimod.extensions import register_node_patch, apply_patches
>>> @register_node_patch("my_node", "pull_distributed")
>>> def empty_distributed(self, vqip):
>>>      return {}

Attributes, methods of the node, and sub-attributes can be patched. Also, an item of a list or a dictionary can be patched if the item argument is provided.

Example of patching an attribute:

10 will be assigned to t:

>>> @register_node_patch("my_node", "t", is_attr=True)
>>> def patch_t(node):
>>>     return 10

Example of patching an attribute item:

patch_default_pull_set_handler will be assigned to pull_set_handler["default"]:

>>> @register_node_patch("my_node", "pull_set_handler", item="default")
>>> def patch_default_pull_set_handler(self, vqip):
>>>     return {}

If patching a method of an attribute, the is_attr argument should be set to True and the target should include the attribute name and the method name, all separated by periods, eg. attribute_name.method_name.

It should be noted that the patched function should have the same signature as the original method or attribute, and the return type should be the same as well, otherwise there will be a runtime error. In particular, the first argument of the patched function should be the node object itself, which will typically be named self.

The overridden method or attribute can be accessed within the patched function using the _patched_{method_name} attribute of the object, eg. self._patched_pull_distributed. The exception to this is when patching an item, in which case the original item is no available to be used within the overriding function.

Finally, the apply_patches is called within the Model.load method and will apply all patches in the order they were registered. This means that users need to be careful with the order of the patches in their extensions files, as they may have interdependencies.

TODO: Update documentation on extensions files.

apply_patches(model)

Apply all registered patches to the model.

TODO: Validate signature of the patched methods and type of patched attributes.

Parameters:

Name	Type	Description	Default
model	Model	The model to apply the patches to.	required

Source code in wsimod\extensions.py

def apply_patches(model: Model) -> None:
    """Apply all registered patches to the model.

    TODO: Validate signature of the patched methods and type of patched attributes.

    Args:
        model (Model): The model to apply the patches to.
    """
    for (node_name, target, item, is_attr), func in extensions_registry.items():
        starget = target.split(".")
        method = starget.pop()

        # Get the member to patch
        node = obj = model.nodes[node_name]
        for attr in starget:
            obj = getattr(obj, attr)

        # Apply the patch
        if item is not None:
            obj = getattr(obj, method)
            obj[item] = func(node) if is_attr else func.__get__(node, node.__class__)
        else:
            setattr(obj, f"_patched_{method}", getattr(obj, method))
            setattr(
                obj, method, func(node) if is_attr else func.__get__(obj, obj.__class__)
            )

register_node_patch(node_name, target, item=None, is_attr=False)

Register a function to patch a node method or any of its attributes.

Parameters:

Name	Type	Description	Default
node_name	str	The name of the node to patch.	required
target	str	The target of the object to patch in the form of a string with the attribute, sub-attribute, etc. and finally method (or attribute) to replace, sepparated with period, eg. make_discharge or sewer_tank.pull_storage_exact.	required
item	Hashable	Typically a string or an integer indicating the item to replace in the selected attribue, which should be a list or a dictionary.	None
is_attr	bool	If True, the decorated function will be called when applying the patch and the result assigned to the target, instead of assigning the function itself. In this case, the only argument passed to the function is the node object.	False

Source code in wsimod\extensions.py

def register_node_patch(
    node_name: str, target: str, item: Hashable = None, is_attr: bool = False
) -> Callable:
    """Register a function to patch a node method or any of its attributes.

    Args:
        node_name (str): The name of the node to patch.
        target (str): The target of the object to patch in the form of a string with the
            attribute, sub-attribute, etc. and finally method (or attribute) to replace,
            sepparated with period, eg. `make_discharge` or
            `sewer_tank.pull_storage_exact`.
        item (Hashable): Typically a string or an integer indicating the item to replace
            in the selected attribue, which should be a list or a dictionary.
        is_attr (bool): If True, the decorated function will be called when applying
            the patch and the result assigned to the target, instead of assigning the
            function itself. In this case, the only argument passed to the function is
            the node object.
    """
    target_id = (node_name, target, item, is_attr)
    if target_id in extensions_registry:
        warnings.warn(f"Patch for {target} already registered.")

    def decorator(func):
        extensions_registry[target_id] = func
        return func

    return decorator