trees

Tools for working with Boolean expression trees.

trees.expr_tree module

An expression tree implementation for Boolean expressions.

class tt.trees.expr_tree.BooleanExpressionTree(postfix_tokens)

Bases: object

An expression tree for Boolean expressions.

This class expects any input it receives to be well-formed; any tokenized lists you pass it directly (instead of from the attribute of the BooleanExpression class) will not be checked.

evaluate(input_dict)

Evaluate the expression held in this tree for specified inputs.

Parameters:input_dict (Dict{str: truthy}) – A dict mapping string variable names to the values for which they should be evaluated. Returns:The result of the expression tree evaluation. Return type:bool

Note

This function does not check to ensure the validity of the input_dict argument in any way.

While you would normally evaluate expressions through the interface provided by the BooleanExpression class, this interface is still exposed for your use if you want to avoid any overhead introduced by the extra layer of abstraction. For example:

>>> from tt import BooleanExpressionTree
>>> bet = BooleanExpressionTree(['A', 'B', 'xor'])
>>> bet.evaluate({'A': 1, 'B': 0})
True
>>> bet.evaluate({'A': 1, 'B': 1})
False

postfix_tokens

The tokens, in postfix order, from which this tree was built.

Type:List[str]

root

The root of the tree; this is None for an empty tree.

Type:ExpressionTreeNode

trees.tree_node module

A node, and related classes, for use in expression trees.

class tt.trees.tree_node.BinaryOperatorExpressionTreeNode(operator_str, l_child, r_child)

Bases: tt.trees.tree_node.ExpressionTreeNode

An expression tree node for binary operators.

operator

The actual operator object wrapped in this node.

Type:BooleanOperator

class tt.trees.tree_node.ExpressionTreeNode(symbol_name, l_child=None, r_child=None)

Bases: object

A base class for expression tree nodes.

evaluate(input_dict)

Recursively evaluate this node.

This is an interface that should be defined in sub-classes.

Parameters:input_dict (Dict{str: truthy}) – A dictionary mapping expression symbols to the value for which they should be subsituted in expression evaluation.

Note

Node evaluation does no checking of the validity of inputs; they should be check before being passed here.

Returns:The evaluation of the tree rooted at this node. Return type:bool

l_child

This node’s left child; None indicates the absence of a child.

Type:ExpressionTreeNode, optional

r_child

This node’s left child; None indicates the absence of a child.

Type:ExpressionTreeNode, optional

symbol_name

The string operator/operand name wrapped in this node.

Type:str

class tt.trees.tree_node.OperandExpressionTreeNode(operand_str)

Bases: tt.trees.tree_node.ExpressionTreeNode

An expression tree node for operands.

Nodes of this type will always be leaves in an expression tree.

class tt.trees.tree_node.UnaryOperatorExpressionTreeNode(operator_str, l_child)

Bases: tt.trees.tree_node.ExpressionTreeNode

An expression tree node for unary operators.

operator

The actual operator object wrapped in this node.

Type:BooleanOperator