Clever Geek Handbook

Python checks if items are in a list

I am trying to iterate over two lists and check if the items in list_1 are in list_2. If the item in list_1 is in list_2, I would like to print the item in list_2. If the item is NOT in list_2, I would like to print the item from list_1. The following code partially accomplishes this, but since I am doing two loops, I get duplicate list_1 values. Can you guide me on the pythonic path?

list_1 = ['A', 'B', 'C', 'D', 'Y', 'Z']
list_2 = ['Letter A',
          'Letter C',
          'Letter D',
          'Letter H',
          'Letter I',
          'Letter Z']

for i in list_1:
    for x in list_2:
        if i in x:
            print(x)
        else:
            print(i)

Current output:

Letter A
A
A
A
A
A
B
B
B
B
B
B
C
Letter C
C
C
C
C
D
D
Letter D
D
D
D
Y
Y
Y
Y
Y
Y
Z
Z
Z
Z
Z
Letter Z

Desired output:

Letter A
B
Letter C
Letter D
Y
Letter Z
+3


source to share


4 answers


You can write:

for i in list_1:
    found = False
    for x in list_2:
        if i in x:
            found = True
            break
    if found:
        print(x)
    else:
        print(i)

The above approach ensures that you either print x

or i

and we only print one value for each item in list_1

.



You can also write (which is the same as above, but uses the ability to add a loop else

to the loop for

):

for i in list_1:
    for x in list_2:
        if i in x:
            print(x)
            break
    else:
        print(i)
+2


source 


for i in list_1:
    found = False
    for x in list_2:
        if i in x:
            found = True
            print(x)
    if found == False:
        print(i)


+1


source


Oneliner:

[print(i) for i in ["Letter {}".format(i) if "Letter {}".format(i) in list_2 else i for i in list_1]]

Outputs:

Letter A
B
Letter C
Letter D
Y
Letter Z
0


source 


for i in range(len(list_1)):
  if list_1[i] in list_2[i]:
    print(list_2[i])
  else:
    print(list_1[i])
-2


source






More articles:


All Articles