UserSpace.set_formula#

UserSpace.set_formula(formula)[source]#

Set the parameter formula for this space.

Defines a formula that determines how this space creates ItemSpace instances when accessed with arguments. The formula’s parameters become the space’s parameters, and its return value can control ItemSpace creation.

Formula Return Values:

None (default): Use this space as base with default behavior
dict: Specify 'base' space and/or 'refs' for ItemSpace

Warning

Controlling base space and references via the return value of the formula is experimental and may lead to unexpected behavior. This feature is not reflected in exported models.

Parameters:: formula (callable or str) – A function or lambda expression that defines the parameters. Can return None or a dict with ‘base’ and ‘refs’ keys.

Example

Below is an example of setting a parameter formula by set_formula:

>>> space = model.new_space('Projection')

>>> space.set_formula(lambda product, scenario: None)
>>> space.parameters
('product', 'scenario')
>>> item = space['ProductA', 'Base']

This is equivalent to setting the formula via the parameters property:

>>> spce.parameters = ('product', 'scenario')
>>> space.parameters
('product', 'scenario')
>>> space.formula
lambda product, scenario: None

The formula can also return a dict to control ItemSpace creation. This is an exprimental feature and not supported in exported models:

>>> space.new_space('BaseA')
>>> space.new_space('BaseB')

>>> def select_base(product_type):
...     if product_type == 'A':
...         return {'base': BaseA}
...     else:
...         return {'base': BaseB}

>>> space.set_formula(select_base)
>>> item_a = space['A']  # Uses BaseA as base space
>>> item_b = space['B']  # Uses BaseB as base space