51 lines
1.6 KiB
Python
51 lines
1.6 KiB
Python
from abc import ABCMeta, abstractmethod
|
|
|
|
|
|
class Visitor(metaclass=ABCMeta):
|
|
"""
|
|
Abstract Visitor class as part of the Visitor Design Pattern.
|
|
"""
|
|
def visit(self, node, *args, **kwargs):
|
|
"""
|
|
Visit the visitor with some object.
|
|
|
|
@param node: An object to call a visitor method with.
|
|
@param args: Arguments to go with the visitor method call.
|
|
@param kwargs: Keyword arguments to go with the visitor method call.
|
|
@return: The return value of the method that was called for visiting object.
|
|
"""
|
|
method = None
|
|
for cls in node.__class__.__mro__:
|
|
method_name = 'visit_'+cls.__name__.lower()
|
|
method = getattr(self, method_name, None)
|
|
if method:
|
|
break
|
|
|
|
if not method:
|
|
method = self.generic_visit
|
|
return method(node, *args, **kwargs)
|
|
|
|
@abstractmethod
|
|
def generic_visit(self, node, *args, **kwargs):
|
|
"""
|
|
The method to call if no methods were found for a visiting object.
|
|
|
|
@param node: An object to call a visitor method with.
|
|
@param args: Arguments to go with the visitor method call.
|
|
@param kwargs: Keyword arguments to go with the visitor method call.
|
|
"""
|
|
|
|
|
|
class Visitee(object):
|
|
"""
|
|
A base class for objects that wish to be able to visit a Visitor class.
|
|
"""
|
|
def accept(self, visitor):
|
|
"""
|
|
Visit a visitor with this class instance.
|
|
|
|
@param visitor: The visitor to visit.
|
|
@type visitor: Visitor
|
|
"""
|
|
return visitor.visit(self)
|