python-patterns/visitor.py at master · Bot123123/python-patterns · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
"""http://peter-hoffmann.com/2010/extrinsic-visitor-pattern-python-inheritance.html"""


classNode(object):
pass


classA(Node):
pass


classB(Node):
pass


classC(A, B):
pass


classVisitor(object):

defvisit(self, node, *args, **kwargs):
meth=None
forclsinnode.__class__.__mro__:
meth_name='visit_'+cls.__name__
meth=getattr(self, meth_name, None)
ifmeth:
break

ifnotmeth:
meth=self.generic_visit
returnmeth(node, *args, **kwargs)

defgeneric_visit(self, node, *args, **kwargs):
print('generic_visit '+node.__class__.__name__)

defvisit_B(self, node, *args, **kwargs):
print('visit_B '+node.__class__.__name__)


a=A()
b=B()
c=C()
visitor=Visitor()
visitor.visit(a)
visitor.visit(b)
visitor.visit(c)

### OUTPUT ###
# generic_visit A
# visit_B B
# visit_B C