ast

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

Functions

is_natural_number(value)

Check whether value is a natural number (i.e. a whole, non-negative number). This can, for example, be used to check if a floating point number such as 3.0 can safely be converted to an integer without loss of information.

Parameters:value – The value to check. This value is a native Python type. Returns:Whether or not the value is a natural number. Return type:bool

is_numeric(value)

Check whether value is a numeric value (i.e. capable of being represented as a floating point value without loss of information).

Parameters:value – The value to check. This value is a native Python type. Returns:Whether or not the value is numeric. Return type:bool

is_real_number(value)

Check whether value is a real number (i.e. capable of being represented as a floating point value without loss of information as well as being finite). Despite being able to be represented as a float, NaN is not considered a real number for the purposes of this function.

Parameters:value – The value to check. This value is a native Python type. Returns:Whether or not the value is a natural number. Return type:bool

Classes

class DataType

Bases: enum.Enum

A collection of constants representing the different supported data types.

BOOLEAN

DATETIME

FLOAT

NULL

STRING

classmethod from_type(python_type)

Get the supported data type constant for the specified Python type. If the type can not be mapped to a supported data type, then a ValueError exception will be raised. This function will not return UNDEFINED.

Parameters:python_type (type) – The native Python type to retrieve the corresponding type constant for. Returns:One of the constants.

classmethod from_value(python_value)

Get the supported data type constant for the specified Python value. If the value can not be mapped to a supported data type, then a TypeError exception will be raised. This function will not return UNDEFINED.

Parameters:python_value – The native Python value to retrieve the corresponding data type constant for. Returns:One of the constants.

UNDEFINED = None

Undefined values. This constant can be used to indicate that a particular symbol is valid, but it’s data type is currently unknown.

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.

evaluate(thing)

Evaluate this AST node and all applicable children nodes.

Parameters:thing – The object to use for symbol resolution. Returns:The result of the evaluation as a native Python type.

reduce()

Reduce this expression into a smaller subset of nodes. If the expression can not be reduced, then return an instance of itself, otherwise return a reduced ExpressionBase to replace it.

Returns:Either a reduced version of this node or itself. Return type:ExpressionBase

result_type = None

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(context, type_, left, right)

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 = 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 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 BooleanExpression(context, value)

Bases: rule_engine.ast.LiteralExpressionBase

Literal boolean expressions representing True or False.

result_type = BOOLEAN

class FloatExpression(context, value)

Bases: rule_engine.ast.LiteralExpressionBase

Literal float expressions representing numerical values.

result_type = FLOAT

class NullExpression(context)

Bases: rule_engine.ast.LiteralExpressionBase

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

result_type = NULL

class StringExpression(context, value)

Bases: rule_engine.ast.LiteralExpressionBase

Literal string expressions representing an array of characters.

result_type = STRING

Miscellaneous Expressions

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 = UNDEFINED

A collection of constants representing the different supported data types.

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

result_type = UNDEFINED