Storing Instances of Objects in a Nested Dictionary

[nkyaelly]

Hi People,

I am getting frustrated with the way Python handles its dictionary.

I have a scenarion where a class A is stored in a dictionary. The class A contains a dictionary B as a field as below

class B:
    bName = ""

class A:
    aName = ""
    b = {}

    def AddB(self, bKey, bVal):
        newB = B()
        newB.bName = bVal
        self.b[bKey] = newB
    
aList = {}


#Now i attempt to add an instance of A into the dictionary the instance #containing a element in B as below.

a1 = A()
a1.name = "first"
a1.AddB("firstValKey", "firstVal")
aList["firstKey"] = a1

# I add another instance of A into the the dictionary. Notice hear no element in # B is set
a2 = A()
a2.name = "second"
aList["secondKey"] = a2

# Then i print out the contents
for aKey, aValue in aList.iteritems():
    print aKey + "_" + aValue.aName
    for bKey, bValue in aValue.b.iteritems():
      print bKey + "_" + bValue.bName
    print "NEXT"

# ERROR: I get this result.
secondKey_
_firstValKey_fi rstVal
NEXT
firstKey_
_firstValKey_fi rstVal
NEXT

#EXPECTED RESULT
secondKey_
NEXT
firstKey_
_firstValKey_fi rstVal
NEXT


Question: Can you help me get the desired result. Would be very much appreciated

[KaezarRex]

Hi People,

I am getting frustrated with the way Python handles its dictionary.

I have a scenarion where a class A is stored in a dictionary. The class A contains a dictionary B as a field as below

class B:
    bName = ""

class A:
    aName = ""
    b = {}

    def AddB(self, bKey, bVal):
        newB = B()
        newB.bName = bVal
        self.b[bKey] = newB
    
aList = {}


#Now i attempt to add an instance of A into the dictionary the instance #containing a element in B as below.

a1 = A()
a1.name = "first"
a1.AddB("firstValKey", "firstVal")
aList["firstKey"] = a1

# I add another instance of A into the the dictionary. Notice hear no element in # B is set
a2 = A()
a2.name = "second"
aList["secondKey"] = a2

# Then i print out the contents
for aKey, aValue in aList.iteritems():
    print aKey + "_" + aValue.aName
    for bKey, bValue in aValue.b.iteritems():
      print bKey + "_" + bValue.bName
    print "NEXT"

# ERROR: I get this result.
secondKey_
_firstValKey_fi rstVal
NEXT
firstKey_
_firstValKey_fi rstVal
NEXT

#EXPECTED RESULT
secondKey_
NEXT
firstKey_
_firstValKey_fi rstVal
NEXT


Question: Can you help me get the desired result. Would be very much appreciated

It looks like the dictionary "b" in class "A" is shared with every instance of class "A". I don't know the exact reason for this, but it might have something to do with the items in the dictionary being stored by reference. To fix your problem, modify class "A".
[CODE=python]class A:

aName = ""

def __init__(self):
self.b = {}

def AddB(self, bKey, bVal):
newB = B()
newB.bName = bVal
self.b[bKey] = newB[/CODE]

[nkyaelly]

It worked like a charm. Many thanks ++

[bvdet]

Hi People,

I am getting frustrated with the way Python handles its dictionary.

I have a scenarion where a class A is stored in a dictionary. The class A contains a dictionary B as a field as below

class B:
    bName = ""

class A:
    aName = ""
    b = {}

    def AddB(self, bKey, bVal):
        newB = B()
        newB.bName = bVal
        self.b[bKey] = newB
    
aList = {}


#Now i attempt to add an instance of A into the dictionary the instance #containing a element in B as below.

a1 = A()
a1.name = "first"
a1.AddB("firstValKey", "firstVal")
aList["firstKey"] = a1

# I add another instance of A into the the dictionary. Notice hear no element in # B is set
a2 = A()
a2.name = "second"
aList["secondKey"] = a2

# Then i print out the contents
for aKey, aValue in aList.iteritems():
    print aKey + "_" + aValue.aName
    for bKey, bValue in aValue.b.iteritems():
      print bKey + "_" + bValue.bName
    print "NEXT"

# ERROR: I get this result.
secondKey_
_firstValKey_fi rstVal
NEXT
firstKey_
_firstValKey_fi rstVal
NEXT

#EXPECTED RESULT
secondKey_
NEXT
firstKey_
_firstValKey_fi rstVal
NEXT


Question: Can you help me get the desired result. Would be very much appreciated

Dictionary 'b' is a class variable. Instead of[code=Python]self.b[bKey] = newB[/code]it would be proper to do this:[code=Python]A.b[bKey] = newB[/code]Class variables are shared among all instances of that class. By creating dictionary 'b' in A.__init__() as KaezarRex suggested, it is an instance variable.