it must be a very stupid question but I cannot find out the explanation
for my code's behaviour, so any help would really be appreciated.
My purpose was, simply put, to have a tree-like data structure, thanks
to the following (simplified to track the issue) Node class :
class Node:
def __init__( self, newContent = None ) :
"""Creates an empty node with no child node."""
self.content = newContent
self.children = []
def __repr__( self ):
"""Returns a textual representation of this node's state."""
res = "Node has "
if self.content:
res += "content (%s)" % ( self.content, )
else:
res += "no content"
res += " and it has "
if self.children:
res += "%s child(ren) : <%s>" % ( len( self.children ),self.children )
else:
res += "no child."
return res
def addChild( self, aChild ):
"""Adds a child to current node."""
self.children.append( aChild )
I test the class simply thanks to :
a=Node()
b=Node()
print a
print b
a.addChild( b )
print a
print b
and it returns, as expected :
a=Node()
b=Node()
a Node has no content and it has no child. b Node has no content and it has no child. a.addChild( b )
a Node has no content and it has 1 child(ren) : <[Node has no content and
it has no child.]> b Node has no content and it has no child.
That is ok. But if I swap the previous __init__ method with my first
version :
def __init__( self, newContent = None, newChildren = [] ) :
"""Creates an empty node with no child node."""
self.content = newContent
self.children = newChildren
and I apply the same test, I got (output not edited) :
a=Node()
b=Node()
a Node has no content and it has no child. b Node has no content and it has no child. a.addChild( b)
a Node has no content and it has 1 child(ren) : <[Node has no content and
it has 1 child(ren) : <[...]>]> b Node has no content and it has 1 child(ren) : <[Node has no content and
it has 1 child(ren) : <[...]>]>
I do not understand why using an empty list as default parameter results
in such a different behaviour.
Thanks in advance for any hint,
kind regards,
Olivier.
PS : tested with python 2.2.1 and 2.3.3. The test should be relevant since :
diff ok.py ko.py 2,4c2,4
<
<
< def __init__( self, newContent = None ) :
---
def __init__( self, newContent = None, newChildren = [] ) : 7c7
< self.children = []
--- self.children = newChildren
Olivier.
