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_firstVal
NEXT
firstKey_
_firstValKey_firstVal
NEXT

#EXPECTED RESULT
secondKey_
NEXT
firstKey_
_firstValKey_firstVal
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_firstVal
NEXT
firstKey_
_firstValKey_firstVal
NEXT

#EXPECTED RESULT
secondKey_
NEXT
firstKey_
_firstValKey_firstVal
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".

class A:
 
    aName = ""
 
    def __init__(self):
        self.b = {}
 
    def AddB(self, bKey, bVal):
        newB = B()
        newB.bName = bVal
        self.b[bKey] = newB

[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_firstVal
NEXT
firstKey_
_firstValKey_firstVal
NEXT

#EXPECTED RESULT
secondKey_
NEXT
firstKey_
_firstValKey_firstVal
NEXT


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

Dictionary 'b' is a class variable. Instead of

self.b[bKey] = newB

it would be proper to do this:

A.b[bKey] = newB

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.