Comparing Python list values to dictionary keys

Question

I am trying to create a new list by comparing the list items to dictionary keys, if the match is found then i append a value of dictionary to new list that was globally initialized. the code i am trying is as below

dict_1 = {'OMSS': '10.1.1.0/24', 'A&A': '10.1.2.0/24', 'AFM': '10.1.3.0/24', 'ATM': '10.1.4.0/24'}
list_1 = ['A&A', 'A&A', 'OMSS', 'OMSS', 'A&A', 'AFM', 'A&A', 'AFM', 'A&A']
list_2 = ['OMSS ', 'OMSS ', 'A&A ', 'A&A ', 'AFM ', 'A&A ', 'AFM ', 'A&A ', 'AFM ']

list_of_list1 = []

for s1 in list_1:
    #print (s2)
    for key, value in dict_1.items():
        #print (key)
        if s1 == key:
            list_of_list1.append(value)

print (list_of_list1)

list_of_list2 = []

for s2 in list_2:
    #print (s2)
    for key, value in dict_1.items():
        #print (key)
        if s2 == key:
            list_of_list2.append(value)

print (list_of_list2)

when i run this i get below output

['10.1.2.0/24', '10.1.2.0/24', '10.1.1.0/24', '10.1.1.0/24', '10.1.2.0/24', '10.1.3.0/24', '10.1.2.0/24', '10.1.3.0/24', '10.1.2.0/24']
{'OMSS': '10.1.1.0/24', 'A&A': '10.1.2.0/24', 'AFM': '10.1.3.0/24', 'ATM': '10.1.4.0/24'}
[]

i am trying to figure out why "list_of_list2" is coming out as empty?

Well, what are some differences between the strings in list_1 and list_2? — ForceBru
– ForceBru, Commented Feb 8, 2021 at 6:36
You'll want to use if s2.strip() == key: (although there are simpler ways to do what you're doing, this would fix your code) — Grismar
– Grismar, Commented Feb 8, 2021 at 6:38

madbird · Accepted Answer · 2021-02-09 06:47:04Z

1

Please stop using containers in most inefficient way. Just use list comprehension:

list_of_list1 = [dict_1[k] for k in list_1 if k in dict_1]

All items of list_2 have ' ' at the end. Indeed they won't be equal to the keys you have in dict_1. Try to strip redundant spaces:

list_of_list2 = [dict_1[k.strip()] for k in list_2 if k.strip() in dict_1]

edited Feb 9, 2021 at 6:47

answered Feb 8, 2021 at 6:46

madbird

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2 Comments

Lakhwinder Smagh Over a year ago

Thanks will try to use list comprehensions

biqarboy Over a year ago

@madbird please update the variable name of 2 from list_of_list1 to list_of_list2.

biqarboy · Accepted Answer · 2021-02-08 06:53:47Z

You need to remove leading and tailing space from the list_2 items to be matched with the dictionary keys. Here is the sample fix of your problem:

dict_1 = {'OMSS': '10.1.1.0/24', 'A&A': '10.1.2.0/24', 'AFM': '10.1.3.0/24', 'ATM': '10.1.4.0/24'}
list_1 = ['A&A', 'A&A', 'OMSS', 'OMSS', 'A&A', 'AFM', 'A&A', 'AFM', 'A&A']
list_2 = ['OMSS ', 'OMSS ', 'A&A ', 'A&A ', 'AFM ', 'A&A ', 'AFM ', 'A&A ', 'AFM ']

list_of_list1 = []

for s1 in list_1:
    #print (s2)
    for key, value in dict_1.items():
        #print (key)
        if s1 == key:
            list_of_list1.append(value)

print (list_of_list1)

list_of_list2 = []

for s2 in list_2:
    #print (s2)
    for key, value in dict_1.items():
        #print (key)
        if s2.strip() == key:
            list_of_list2.append(value)

print (list_of_list2)

Output:

['10.1.2.0/24', '10.1.2.0/24', '10.1.1.0/24', '10.1.1.0/24', '10.1.2.0/24', '10.1.3.0/24', '10.1.2.0/24', '10.1.3.0/24', '10.1.2.0/24']
['10.1.1.0/24', '10.1.1.0/24', '10.1.2.0/24', '10.1.2.0/24', '10.1.3.0/24', '10.1.2.0/24', '10.1.3.0/24', '10.1.2.0/24', '10.1.3.0/24']

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