Find mismatch item on same index in two list in Python

Sometimes we need to compare elements in two Python lists based on both their value and position. This article shows different methods to find indices where elements at the same position have different values.

Using for Loop

We can design a for loop to compare values at similar indexes. If the values do not match, we add the index to a result list ?

listA = [13, 'Mon', 23, 62, 'Sun']
listB = [5, 'Mon', 23, 6, 'Sun']

# Index variable
idx = 0

# Result list
res = []

# With iteration
for i in listA:
    if i != listB[idx]:
        res.append(idx)
    idx = idx + 1

# Result
print("The index positions with mismatched values:\n", res)

The index positions with mismatched values:
[0, 3]

Using zip() Function

The zip() function helps us write shorter code by pairing elements from each list. However, there's an issue with the previous approach - it finds the first occurrence index, not the actual position ?

listA = [13, 'Mon', 23, 62, 'Sun']
listB = [5, 'Mon', 23, 6, 'Sun']

# Correct approach using zip with enumerate
res = [idx for idx, (a, b) in enumerate(zip(listA, listB)) if a != b]

# Result
print("The index positions with mismatched values:\n", res)

The index positions with mismatched values:
[0, 3]

Using enumerate() Function

This approach uses enumerate() to get both index and element, then compares with the corresponding element in the other list ?

listA = [13, 'Mon', 23, 62, 'Sun']
listB = [5, 'Mon', 23, 6, 'Sun']

res = [idx for idx, elem in enumerate(listB)
       if elem != listA[idx]]

# Result
print("The index positions with mismatched values:\n", res)

The index positions with mismatched values:
[0, 3]

Comparison

Conclusion

Use zip() with enumerate() for the most Pythonic solution. Use enumerate() for simple cases, and basic for loops when learning Python fundamentals.