ExpressionValueVisitor

(class from pyomo.core.expr.visitor)

class pyomo.core.expr.visitor.ExpressionValueVisitor

Bases: object

Note

This class is a customization of the PyUtilib ValueVisitor class that is tailored to efficiently walk Pyomo expression trees. However, this class is not a subclass of the PyUtilib ValueVisitor class because all key methods are reimplemented.

__init__()

Methods

__init__()
dfs_postorder_stack(node)	Perform a depth-first search in postorder using a stack implementation.
finalize(ans)	This method defines the return value for the search methods in this class.
visit(node, values)	Visit a node in a tree and compute its value using the values of its children.
visiting_potential_leaf(node)	Visit a node and return its value if it is a leaf.

Member Documentation

dfs_postorder_stack(node)

Perform a depth-first search in postorder using a stack implementation.

Note

This method has the same functionality as the PyUtilib ValueVisitor.dfs_postorder_stack method. The difference is that this method is tailored to efficiently walk Pyomo expression trees.

Parameters:

node – The root node of the expression tree that is searched.

Returns:

The return value is determined by the finalize() function, which may be defined by the user.

finalize(ans)

This method defines the return value for the search methods in this class.

The default implementation returns the value of the initial node (aka the root node), because this visitor pattern computes and returns value for each node to enable the computation of this value.

Parameters:

ans – The final value computed by the search method.

Returns:

The final value after the search. Defaults to simply returning ans.

visit(node, values)

Visit a node in a tree and compute its value using the values of its children.

This method should be over-written by a user that is creating a sub-class.

Parameters:

• node – a node in a tree

• values – a list of values of this node’s children

Returns:

The value for this node, which is computed using values

visiting_potential_leaf(node)

Visit a node and return its value if it is a leaf.

Note

This method needs to be over-written for a specific visitor application.

Parameters:

node – a node in a tree

Returns:

(flag, value). If flag is False, then the node is not a leaf and value is None. Otherwise, value is the computed value for this node.

Return type:

A tuple