142 lines
5.1 KiB
Python
142 lines
5.1 KiB
Python
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"""Generic visitor pattern implementation for Python objects."""
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import enum
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class Visitor(object):
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defaultStop = False
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@classmethod
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def _register(celf, clazzes_attrs):
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assert celf != Visitor, "Subclass Visitor instead."
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if "_visitors" not in celf.__dict__:
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celf._visitors = {}
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def wrapper(method):
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assert method.__name__ == "visit"
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for clazzes, attrs in clazzes_attrs:
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if type(clazzes) != tuple:
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clazzes = (clazzes,)
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if type(attrs) == str:
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attrs = (attrs,)
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for clazz in clazzes:
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_visitors = celf._visitors.setdefault(clazz, {})
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for attr in attrs:
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assert attr not in _visitors, (
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"Oops, class '%s' has visitor function for '%s' defined already."
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% (clazz.__name__, attr)
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)
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_visitors[attr] = method
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return None
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return wrapper
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@classmethod
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def register(celf, clazzes):
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if type(clazzes) != tuple:
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clazzes = (clazzes,)
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return celf._register([(clazzes, (None,))])
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@classmethod
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def register_attr(celf, clazzes, attrs):
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clazzes_attrs = []
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if type(clazzes) != tuple:
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clazzes = (clazzes,)
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if type(attrs) == str:
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attrs = (attrs,)
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for clazz in clazzes:
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clazzes_attrs.append((clazz, attrs))
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return celf._register(clazzes_attrs)
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@classmethod
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def register_attrs(celf, clazzes_attrs):
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return celf._register(clazzes_attrs)
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@classmethod
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def _visitorsFor(celf, thing, _default={}):
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typ = type(thing)
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for celf in celf.mro():
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_visitors = getattr(celf, "_visitors", None)
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if _visitors is None:
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break
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m = celf._visitors.get(typ, None)
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if m is not None:
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return m
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return _default
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def visitObject(self, obj, *args, **kwargs):
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"""Called to visit an object. This function loops over all non-private
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attributes of the objects and calls any user-registered (via
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@register_attr() or @register_attrs()) visit() functions.
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If there is no user-registered visit function, of if there is and it
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returns True, or it returns None (or doesn't return anything) and
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visitor.defaultStop is False (default), then the visitor will proceed
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to call self.visitAttr()"""
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keys = sorted(vars(obj).keys())
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_visitors = self._visitorsFor(obj)
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defaultVisitor = _visitors.get("*", None)
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for key in keys:
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if key[0] == "_":
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continue
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value = getattr(obj, key)
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visitorFunc = _visitors.get(key, defaultVisitor)
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if visitorFunc is not None:
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ret = visitorFunc(self, obj, key, value, *args, **kwargs)
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if ret == False or (ret is None and self.defaultStop):
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continue
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self.visitAttr(obj, key, value, *args, **kwargs)
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def visitAttr(self, obj, attr, value, *args, **kwargs):
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"""Called to visit an attribute of an object."""
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self.visit(value, *args, **kwargs)
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def visitList(self, obj, *args, **kwargs):
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"""Called to visit any value that is a list."""
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for value in obj:
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self.visit(value, *args, **kwargs)
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def visitDict(self, obj, *args, **kwargs):
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"""Called to visit any value that is a dictionary."""
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for value in obj.values():
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self.visit(value, *args, **kwargs)
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def visitLeaf(self, obj, *args, **kwargs):
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"""Called to visit any value that is not an object, list,
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or dictionary."""
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pass
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def visit(self, obj, *args, **kwargs):
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"""This is the main entry to the visitor. The visitor will visit object
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obj.
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The visitor will first determine if there is a registered (via
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@register()) visit function for the type of object. If there is, it
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will be called, and (visitor, obj, *args, **kwargs) will be passed to
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the user visit function.
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If there is no user-registered visit function, of if there is and it
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returns True, or it returns None (or doesn't return anything) and
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visitor.defaultStop is False (default), then the visitor will proceed
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to dispatch to one of self.visitObject(), self.visitList(),
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self.visitDict(), or self.visitLeaf() (any of which can be overriden in
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a subclass)."""
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visitorFunc = self._visitorsFor(obj).get(None, None)
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if visitorFunc is not None:
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ret = visitorFunc(self, obj, *args, **kwargs)
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if ret == False or (ret is None and self.defaultStop):
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return
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if hasattr(obj, "__dict__") and not isinstance(obj, enum.Enum):
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self.visitObject(obj, *args, **kwargs)
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elif isinstance(obj, list):
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self.visitList(obj, *args, **kwargs)
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elif isinstance(obj, dict):
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self.visitDict(obj, *args, **kwargs)
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else:
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self.visitLeaf(obj, *args, **kwargs)
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