pyvisitor

An implementation of the visitor pattern for Python.

Find more details at Follow-Up to Python Visitor.

Works on both Python 2 and 3. Specifically tested on 2.7.2, 2.7.5, 3.3.2, 3.3.5, and 3.4.0.

usage

First, import the module.

import visitor

Then, define a class that you want to act as the visitor.

class SomeVisitor(object):
  pass

Then, mark the method and parameter that provides dynamic dispatching.

class SomeVisitor(object):
  @visitor.on('node') # Note the name of the parameter in the on decorator
  def visit(self, node):
    pass

Now, override the method on classes that you want called specifically based on the type of the argument.

class SomeVisitor(object):
  @visitor.on('node') # Note the name of the parameter in the on decorator
  def visit(self, node):
    pass

  @visitor.when(MyFirstClass)
  def visit(self, node):
    print 'I am going first class!'

  @visitor.when(MyOtherClass)
  def visit(self, node):
    print 'Whatever. Boring.'

run the example

> git clone git@github.com:realistschuckle/pyvisitor.git
> cd pyvisitor
> python example
Creating the abstract syntax tree that contains x = 5
and printing it
x=5

Creating me and my dependents and printing them
- Curtis
  - Son
  - Daughter
  - Lola a Shitzu