How to add multiple values to dictionary keys in Python

Question

I am trying to add a value (string) to the dictionary I already have in this form:

item1
item2
item3

    myDictionary = {'key':[item1, item2]}

    ###Adding the third value (item3) to the already {'key': ['item1', 'item2']} dictionary.

    myDictionary['key'] = [myDictionary['key'], item3]

    ###Ending with 3rd item being placed as a separate list of values:
    #{'key': [['item1', 'item2'], item3]} 
    #instead of getting the expected and desirable:

    {'key': ['item1', 'item2', 'item3']}

Already tried the How to add multiple values in dictionary having specific key solution as myDictionary[key].append(value) would yell a AttributeError: *str* object has no attribute *append* Error so using [myDictionary['key'], item3] was the way to add the second but not the third value for the key, key.

As requested, this is the actual code that I am trying to run:

currHostDict = {}
for x in netstatinfo:
    result = open("result.txt", "a+")
    z = re.match("^en", x)
    if z:
        adapter = re.split(" +", x)[0]
        macIp = re.split(" +", x)[3]
        if adapter in currHostDict:
            #currHostDict[adapter] = [currHostDict[adapter], macIp]
            print(type(currHostDict))
            currHostDict[adapter].extend([macIp])
            #currHostDict[adapter] = [currHostDict[adapter].extend(macIp)]
            #currHostDict[adapter] = [currHostDict[adapter].append(macIp)]
            #currHostDict[adapter] = "test"
        else:
            currHostDict[adapter] = macIp

And this one issues a AttributeError: 'str' object has no attribute 'extend'error

I can also confirm that running this simplified code:

item1 = "item1"
item2 = "item2"
item3 = "item3"

currHostDict = {'en0':[item1,item2]}

currHostDict['en0'].extend([item3])

print(currHostDict)

outputs the expected {'en0': ['item1', 'item2', 'item3']} .

However, this assumes the dictionary already has at least one key and at least one value for that key as I am creating in the original code through currHostDict[adapter] = macIp

Please also note that the else statement will always run first so the dictionary is always filled out with at least one key and its value.

Answer 1

In your code, the problem comes from the line:

            currHostDict[adapter] = macIp

Because macIp is a str and not a list of str . The obvious fix is the following:

            currHostDict[adapter] = [macIp]

Moreover, I advise you to check the defaultdict structure. If you request a non-existent key in a defaultdict, it will initialize it with the given default value.

from collections import defaultdict

netstatinfo = ["A - - item1", "B - - item4", "A - - item2", "A - - item3"]

currHostDict = defaultdict(lambda: [])
for x in netstatinfo:
    adapter = re.split(" +", x)[0]
    macIp = re.split(" +", x)[3]
    currHostDict[adapter].append(macIp)

print(dict(currHostDict))
# {'A': ['item1', 'item2', 'item3'], 'B': ['item4']}