Python – Extract rows with Even length strings

When working with nested lists of strings, you may need to extract rows where all strings have even length. This can be accomplished using list comprehension with the all() function and modulus operator %.

Syntax

result = [row for row in nested_list if all(len(element) % 2 == 0 for element in row)]

How It Works

The solution uses three key components ?

• len(element) % 2 == 0 − Checks if string length is even
• all() − Returns True only if all elements in the row have even length
• List comprehension − Filters and collects rows that meet the condition

Example

data = [["python", "is", "best"], ["best", "good", "python"], ["is", "better"], ["for", "coders"]]

print("The list is:")
print(data)

result = [row for row in data if all(len(element) % 2 == 0 for element in row)]

print("The resultant list is:")
print(result)

The list is:
[['python', 'is', 'best'], ['best', 'good', 'python'], ['is', 'better'], ['for', 'coders']]
The resultant list is:
[['python', 'is', 'best'], ['best', 'good', 'python'], ['is', 'better']]

Step-by-Step Analysis

Let's examine why each row is included or excluded ?

data = [["python", "is", "best"], ["best", "good", "python"], ["is", "better"], ["for", "coders"]]

for i, row in enumerate(data):
    print(f"Row {i}: {row}")
    lengths = [len(element) for element in row]
    print(f"Lengths: {lengths}")
    all_even = all(len(element) % 2 == 0 for element in row)
    print(f"All even: {all_even}\n")

Row 0: ['python', 'is', 'best']
Lengths: [6, 2, 4]
All even: True

Row 1: ['best', 'good', 'python']
Lengths: [4, 4, 6]
All even: True

Row 2: ['is', 'better']
Lengths: [2, 6]
All even: True

Row 3: ['for', 'coders']
Lengths: [3, 6]
All even: False

Alternative Approach Using Filter

You can also use the filter() function for the same result ?

data = [["python", "is", "best"], ["best", "good", "python"], ["is", "better"], ["for", "coders"]]

def has_all_even_lengths(row):
    return all(len(element) % 2 == 0 for element in row)

result = list(filter(has_all_even_lengths, data))
print("Using filter():", result)

Using filter(): [['python', 'is', 'best'], ['best', 'good', 'python'], ['is', 'better']]

Conclusion

Use list comprehension with all() and modulus operator to extract rows where all strings have even length. This approach is both readable and efficient for filtering nested string lists.