How to Filter and De‑duplicate Python Lists Using itertools.chain and List Comprehensions

Hello, I'm an advanced Python user.

1. Introduction

Yesterday in the Python community "NicePlus" a member asked a basic question about processing a list of lists. The original data are:

l1 = [['a','b','c'], [1,2,3], ['c','c','c']]
l2 = [[1,1,1], ['a','a','a'], ['c',0,0,0]]
l3 = [['c','c','c'], [5,6,7], [7,3,4], [0,'a']]

2. Implementation

The first solution uses itertools.chain to iterate over all sub‑lists and a break statement to stop after the first matching element, effectively removing duplicates.

from itertools import chain
l1 = [['a','b','c'], [1,2,3], ['c','c','c']]
l2 = [[1,1,1], ['a','a','a'], ['c',0,0,0]]
l3 = [['c','c','c'], [5,6,7], [7,3,4], [0,'a']]
l = []
for i in chain(l1, l2, l3):
    for j in i:
        if j in ('a','b','c'):
            l.append(i)
            break
print(l)

The output shows the sub‑lists that contain any of the characters 'a', 'b', or 'c'.

An alternative, more compact solution uses a list comprehension:

l1 = [['a','b','c'], [1,2,3], ['c','c','c']]
l2 = [[1,1,1], ['a','a','a'], ['c',0,0,0]]
l3 = [['c','c','c'], [5,6,7], [7,3,4], [0,'a']]
all_list = l1 + l2 + l3
l = []
res = [l.append(i) for i in all_list for j in i if j in ('a','b','c')]
final_res = []
result = [final_res.append(item) for item in l if item not in final_res]
print(final_res)

Although slightly redundant, this version achieves the same result.

3. Summary

The article walks through a common Python list‑handling problem, presents two concrete implementations, and demonstrates how to filter and deduplicate nested lists effectively.