Python list of tuples

Question

L1 = ['A', 'B', 'C', 'D'] L2 = [('A', 10)], ('B', 20)]

Now from these two list how can i generate common elements

output_list = [('A', 10), ('B', 20), ('C', ''), ('D', '')]

How can i get output_list using L1 and L2?

I tried the following

 for i in L2: for j in L1: if i[0] == j: ouput_list.append(i) else: output_list.append((j, ''))

But i'm not getting the exact out which i want

what do you mean with common elements? Common in the sense of position, ASCII-number (i.e. ascending/descending sorting...)? — Lorenz Lo Sauer
– Lorenz Lo Sauer, Commented Jun 4, 2012 at 6:52

BrenBarn · Accepted Answer · 2012-06-04 06:49:33Z

[(k, dict(L2).get(k, '')) for k in L1]

You can pull the dict(L2) out of the list comprehension if you don't want to recalculate it each time (e.g., if L2 is large).

d = dict(L2) [(k, d.get(k, '')) for k in L1]

Lev Levitsky · Accepted Answer · 2012-06-04 06:58:08Z

In case you are sure the order of the lists is right and L2 is always shorter or same length:

from itertools import cycle L2 + zip(L1[len(L2):], cycle(('',)))

2 Answers 2