Associating two item in a list

Question

I am comparing two lists for common strings and my code currently works to output items in common from two lists.

list1

['5', 'orange', '20', 'apple', '50', 'blender'] 

list2

['25', 'blender', '20', 'pear', '40', 'spatula'] 

Here is my code so far:

for item1 in list1[1::2]:     for item2 in list2[1::2]:         if item1 == item2:             print(item1) 

This code would return blender. What I want to do now is to also print the number before the blender in each list to obtain an output similar to:

blender, 50, 25 

I have tried to add two new lines to the for loop but did not have the desired output:

for item1 in list1[1::2]:     for item2 in list2[1::2]:         for num1 in list1[0::2]:             for num2 in list2[0::2]:                if item1 == item2:                    print(item1, num1, num2) 

I know now that making for loops is not the answer. Also trying to call item1[-1] does not work. I am new to Python and need some help with this!

Thank you

Answer 1

You can do it in two ways, either stay with lists (Which is more messy):

list1 = ['5', 'orange', '20', 'apple', '50', 'blender'] list2 = ['25', 'blender', '20', 'pear', '40', 'spatula'] for item1 in list1[1::2]:   for item2 in list2[1::2]:     if item1 == item2:        item_to_print = item1        print(item1, ",", end="")        for index in range(len(list1)):            if list1[index] == item1:                print(list1[index - 1], ",", end="")        for index in range(len(list2)):            if list2[index] == item1:                print(list2[index - 1]) 

or the better way (in my opinion) with dictionary:

dict1 = {'apple': '20', 'blender': '50', 'orange': '5'} dict2 = {'blender': '25', 'pear': '20', 'spatula': '40'} for item in dict1:    if item in dict2:        print(item, ",", dict1[item], ",", dict2[item]) 

Both will output:

>> blender , 50 , 25 

Answer 2

You're approaching this problem with the wrong Data Structure. You shouldn't keep this data in lists if you're doing lookups between the two. Instead, it would be much easier to use a dictionary here.

Setup

You can use zip to create these two dictionaries:

a = ['5', 'orange', '20', 'apple', '50', 'blender'] b = ['25', 'blender', '20', 'pear', '40', 'spatula']  dct_a = dict(zip(a[1::2], a[::2])) dct_b = dict(zip(b[1::2], b[::2])) 

This will leave you with these two dictionaries:

{'orange': '5', 'apple': '20', 'blender': '50'} {'blender': '25', 'pear': '20', 'spatula': '40'} 

---

This makes every part of your problem easier to solve. For example, to find common keys:

common = dct_a.keys() & dct_b.keys() # {'blender'} 

And to find all the values matching each common key:

[(k, dct_a[k], dct_b[k]) for k in common] 

Output:

[('blender', '50', '25')]