Consider the following class:
class Node(object):
def __init__(self, name, parent=None):
self.name = name
self.parent = parent
def _ancestors(self , ants=None):
if ants is None:
ants = []
else:
ants.insert(0, self.name)
if self.parent is None:
return ants
return self.parent._an cestors(ants)
ancestors = property(_ances tors)
The ancestor property generates a list ancestor nodes by having each parent
examine its own name recursively. The recursion is managed by calling the
method underlying the parent property, rather than calling the property
directly.
Is it possible to rewrite this property using decorator syntax? Does the
@property decorator create some underlying method that I can call directly?
Alternately, perhaps there is a way to rewrite the recursion so that such a
call is unnecessary? Note that the property should not add its own name if
it is the originating node (the node trying to find _its_ ancestors). So
something like this didn't work for me:
@property
def ancestors(self) :
if self.parent is None:
return [self.name]
return [self.name] + self.parent.anc estors
In other words, since there is no longer a list passing from child to parent
during the recursion, is there a graceful way to examine the state of the
ancestor list so far?
Thanks,
Jeffrey 2 1682
Jeffrey Froman wrote: it is the originating node (the node trying to find its ancestors). So something like this didn't work for me:
@property def*ancestors(s elf): if*self.parent* is*None: return*[self.name] return*[self.name]*+*self.parent. ancestors
But this will, I suppose:
@property
def ancestors(self) :
if self.parent:
return self.parent.anc estors + [self.parent]
return []
A non-recursive variant:
@property
def ancestors(self) :
result = []
node = self.parent
while node:
result.append(n ode)
node = node.parent
result.reverse( )
return result
Peter
Peter Otten wrote: something like this didn't work for me:
<snip> But this will, I suppose:
@property def ancestors(self) : if self.parent: return self.parent.anc estors + [self.parent] return []
A non-recursive variant:
@property def ancestors(self) : result = [] node = self.parent while node: result.append(n ode) node = node.parent result.reverse( ) return result
Indeed, both of these patterns suit my needs. Thanks very much for the
eye-opening insights.
Jeffrey This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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