CODEWITHSUNDEEP
pythonlistobjectattributes
user3043892
user3043892

Reputation: 1

Python: Object has a list as attribute but stores only a reference and not the list

I work in Python 2.4 (comes with the system). I try to compile a list of objects. Each Object has an attribute that is a list of other objects. Whatever I do it seems to me that the attribute(list) stores only a reference and not the list itself. ControlPoint.LeafPairList is a reference to LeafList but does not contain the List itself.

Later in the script I try to address the LeafPair with ControlPoint.LeafPairList[i] that gives me always the same settings

Any suggestions to make it work? Thanks in advance.

Example:

def ReadControlPoint(fh,ControlPoint):
    line = fh.readline()
    while not line.startswith('}'):
        Scratch = line.split(' = ' )
        if Scratch[0] == 'LeafPairList':

            ReadLeafPairList(fh, LeafList)

            setattr(ControlPoint, 'LeafPairList', LeafList)


        else:
            setattr(ControlPoint, Scratch[0], Scratch[1].strip('\n"'))      
        line = fh.readline()

def ReadLeafPairList(fh, LeafList):
    del LeafList[:]
    line = fh.readline()
    while not line.startswith('}'):
        Scratch = line.split(' = ')
        Scratch = Scratch[1].strip('"\n').split()
        Leafs = LeafPair(Scratch)
        LeafList.append(Leafs)
        line = fh.readline()

The List looks something like that:

Machine = "Infinity_1"
Gantry = " 310.0"
Collimator = "   0.0"
Couch = "   0.0"
Weight = "  29.46 %"
NumberOfControlPoints = " 7"
NumberOfLeafPairs = " 80"
LeavesCanOverlap = " 1"
X2_Value = "   4.5"
X1_Value = "   4.5"
Y1_Value = "   9.0"
Y2_Value = "   9.0"
ControlPointList = {
ControlPoint = {
ControlPoint = " 0"
Weight = "   0.3"
LeftJawPosition = "   4.5"
RightJawPosition = "   4.5"
TopJawPosition = "   9.0"
BottomJawPosition = "   9.0"
LeafPairList = {
LeafPair(0) = "   0.5   0.0   0.5 -19.8"
LeafPair(0) = "   0.5   0.0   0.5 -19.2"
LeafPair(0) = "   0.5   0.0   0.5 -18.8"
LeafPair(0) = "   0.5   0.0   0.5 -18.2"
LeafPair(0) = "   0.5   0.0   0.5 -17.8"

}
}
ControlPoint = {
ControlPoint = " 1"
Weight = "   0.3"
LeftJawPosition = "   4.5"
RightJawPosition = "   4.5"
TopJawPosition = "   9.0"
BottomJawPosition = "   9.0"
LeafPairList = {
LeafPair(1) = "   0.5   0.0   0.5 -19.8"
LeafPair(1) = "   0.5   0.0   0.5 -19.2"
...
}
}
}

Upvotes: 0

Views: 88

Answers (1)

Raydel Miranda
Raydel Miranda

Reputation: 14360

Ok thats because in Python all are references. I'll explain with a simple example:

>>> l = [0, 0, 0]
>>> a = l
>>> a[0] = "Changed"

>>> print (l)
["Changed", 0, 0]
>>> print (a)
["Changed", 0, 0]

This happend because with the statement a=l we have just put another name to the object [0, 0, 0]

To achive what you want you can use copy module

>>> import copy

>>> l = [0, 0, 0]
>>> a = copy.copy(l)  # This is the only change.
>>> a[0] = "Changed"

>>> print (l)
[0, 0, 0]
>>> print (a)
["Changed", 0, 0]

Upvotes: 1

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