7.14. Interpreter

Important

EN: Interpreter
PL: Interpreter
Type: class

The Interpreter design pattern is a behavioral design pattern that specifies how to evaluate sentences in a language. This pattern is used to interpret sentences in a language and represents a grammar as a hierarchy of composite objects.

In Python, we can implement the Interpreter pattern using classes. Here's a simple example:

First, we define an AbstractExpression class that declares an abstract interpret method:

✘>>> class AbstractExpression:
...     def interpret(self):
...         pass

Then, we define a TerminalExpression class that implements the interpret method:

✘>>> class TerminalExpression(AbstractExpression):
...     def interpret(self):
...         print("Terminal expression is being interpreted.")

Finally, we can use the AbstractExpression and TerminalExpression classes like this:

✘>>> class NonterminalExpression(AbstractExpression):
...     def __init__(self, expression):
...         self._expression = expression
...
...     def interpret(self):
...         print("Nonterminal expression is being interpreted.")
...         self._expression.interpret()
...
>>> terminal_expression = TerminalExpression()
>>> nonterminal_expression = NonterminalExpression(terminal_expression)
...
>>> nonterminal_expression.interpret()
Nonterminal expression is being interpreted.
Terminal expression is being interpreted.

In this example, the NonterminalExpression interprets a TerminalExpression.

7.14. Interpreter

7.14.1. Pattern

7.14.2. Problem

7.14.3. Solution

7.14.4. Assignments