ast

This module contains the nodes which comprise the abstract syntax tree generated from parsed grammar text.

Warning

The content of this module should be treated as private.

While the code within this module is documented, it is not meant to be used by consumers of the package. Directly accessing and using any object or function within this module should be done with care. Breaking API changes within this module may not always cause a major version bump. The reason for this is that it is often necessary to update the AST in an API breaking way in order to add new features.

Classes

class Assignment(name, *, value=UNDEFINED, value_type=None)

Bases: object

An internal assignment where by a symbol is populated with a value of the specified type.

__init__(name, *, value=UNDEFINED, value_type=None)

Parameters

• name (str) – The symbol name that the assignment is defining.

• value – The value of the assignment.

• value_type (DataType) – The data type of the assignment.

name

value

value_type

class Statement(context, expression)

Bases: rule_engine.ast.ASTNodeBase

A class representing the top level statement of the grammar text.

Base Classes

class ExpressionBase

Bases: rule_engine.ast.ASTNodeBase

result_type = UNDEFINED

The data type of the result of successful evaluation.

class LeftOperatorRightExpressionBase(context, type_, left, right)

Bases: rule_engine.ast.ExpressionBase

A base class for representing complex expressions composed of a left side and a right side, separated by an operator.

compatible_types

A tuple containing the compatible data types that the left and right expressions must return. This can for example be used to indicate that arithmetic operations are compatible with FLOAT but not STRING values.

__init__(context, type_, left, right)

Parameters

• context (Context) – The context to use for evaluating the expression.

• type (str) – The grammar type of operator at the center of the expression. Subclasses must define operator methods to handle evaluation based on this value.

• left (ExpressionBase) – The expression to the left of the operator.

• right (ExpressionBase) – The expression to the right of the operator.

class LiteralExpressionBase(context, value)

Bases: rule_engine.ast.ExpressionBase

A base class for representing literal values from the grammar text.

__init__(context, value)

Parameters

• context (Context) – The context to use for evaluating the expression.

• value – The native Python value.

Left-Operator-Right Expressions

class ArithmeticExpression(context, type_, left, right)

Bases: rule_engine.ast.LeftOperatorRightExpressionBase

A class for representing arithmetic expressions from the grammar text such as addition and subtraction.

result_type = FLOAT

class ArithmeticComparisonExpression(*args, **kwargs)

Bases: rule_engine.ast.ComparisonExpression

A class for representing arithmetic comparison expressions from the grammar text such as less-than-or-equal-to and greater-than.

result_type = BOOLEAN

class BitwiseExpression(*args, **kwargs)

Bases: rule_engine.ast.LeftOperatorRightExpressionBase

A class for representing bitwise arithmetic expressions from the grammar text such as XOR and shifting operations.

result_type = UNDEFINED

class BitwiseShiftExpression(*args, **kwargs)

Bases: rule_engine.ast.BitwiseExpression

result_type = FLOAT

class ComparisonExpression(context, type_, left, right)

Bases: rule_engine.ast.LeftOperatorRightExpressionBase

A class for representing comparison expressions from the grammar text such as equality checks.

result_type = BOOLEAN

class LogicExpression(context, type_, left, right)

Bases: rule_engine.ast.LeftOperatorRightExpressionBase

A class for representing logical expressions from the grammar text such as “and” and “or”.

result_type = BOOLEAN

class FuzzyComparisonExpression(*args, **kwargs)

Bases: rule_engine.ast.ComparisonExpression

A class for representing regular expression comparison expressions from the grammar text such as search and does not match.

result_type = BOOLEAN

Literal Expressions

class ArrayExpression(*args, **kwargs)

Bases: rule_engine.ast._CollectionMixin, rule_engine.ast.LiteralExpressionBase

Literal array expressions containing 0 or more sub-expressions.

result_type = ARRAY

class BooleanExpression(context, value)

Bases: rule_engine.ast.LiteralExpressionBase

Literal boolean expressions representing True or False.

result_type = BOOLEAN

class DatetimeExpression(context, value)

Bases: rule_engine.ast.LiteralExpressionBase

Literal datetime expressions representing a specific point in time. This expression type always evaluates to true.

result_type = DATETIME

class FloatExpression(context, value, **kwargs)

Bases: rule_engine.ast.LiteralExpressionBase

Literal float expressions representing numerical values.

result_type = FLOAT

class MappingExpression(context, value, **kwargs)

Bases: rule_engine.ast.LiteralExpressionBase

Literal mapping expression representing a set of associations between keys and values.

result_type = MAPPING

class NullExpression(context, value=None)

Bases: rule_engine.ast.LiteralExpressionBase

Literal null expressions representing null values. This expression type always evaluates to false.

result_type = NULL

class SetExpression(*args, **kwargs)

Bases: rule_engine.ast._CollectionMixin, rule_engine.ast.LiteralExpressionBase

Literal set expressions containing 0 or more sub-expressions.

result_type = SET

class StringExpression(context, value)

Bases: rule_engine.ast.LiteralExpressionBase

Literal string expressions representing an array of characters.

result_type = STRING

Miscellaneous Expressions

class ComprehensionExpression(context, result, variable, iterable, condition=None)

Bases: rule_engine.ast.ExpressionBase

result_type = ARRAY

class ContainsExpression(context, container, member)

Bases: rule_engine.ast.ExpressionBase

An expression used to test whether an item exists within a container.

result_type = BOOLEAN

class GetAttributeExpression(context, object_, name, safe=False)

Bases: rule_engine.ast.ExpressionBase

A class representing an expression in which name is retrieved as an attribute of object.

result_type = UNDEFINED

class GetItemExpression(context, container, item, safe=False)

Bases: rule_engine.ast.ExpressionBase

A class representing an expression in which an item is retrieved from a container object.

result_type = UNDEFINED

class GetSliceExpression(context, container, start=None, stop=None, safe=False)

Bases: rule_engine.ast.ExpressionBase

A class representing an expression in which a range of items is retrieved from a container object.

result_type = UNDEFINED

class SymbolExpression(context, name, scope=None)

Bases: rule_engine.ast.ExpressionBase

A class representing a symbol name to be resolved at evaluation time with the help of a Context object.

result_type

class TernaryExpression(context, condition, case_true, case_false)

Bases: rule_engine.ast.ExpressionBase

A class for representing ternary expressions from the grammar text. These involve evaluating condition before evaluating either case_true or case_false based on the results.

result_type = UNDEFINED

class UnaryExpression(context, type_, right)

Bases: rule_engine.ast.ExpressionBase

A class for representing unary expressions from the grammar text. These involve a single operator on the left side.

result_type = UNDEFINED