Constant Values¶

When you are using a pre-existing function for a node, and one or more of the parameters takes a constant value, one way is to define a lambda, which fixes the parameter value. For example, below we use a lambda to fix the second parameter passed to the add function:

>>> def add(x, y):
...    return x + y

>>> comp = Computation()
>>> comp.add_node('a', value=1)
>>> comp.add_node('b', lambda a: add(a, 1))
>>> comp.compute_all()
>>> comp.v.b
2

However providing ConstantValue objects to the args or kwds parameters of add_node, make this simpler. C is an alias for ConstantValue, and in the example below, we use that to tell node b to calculate by taking parameter x from node a, and y as a constant, 1:

>>> comp = Computation()
>>> comp.add_node('a', value=1)
>>> comp.add_node('b', add, kwds={"x": "a", "y": C(1)})
>>> comp.compute_all()
>>> comp.v.b
2