python - List of list increment if exists otherwise extend -

i have list of lists follows

[ ['a', 1], ['b',2], ['c',1], ['a', 2], ['c', 5] ] 

i want normalize list in such way every, 'a', 'b', 'c' etc, have 1 unique entry in list, , every duplicate list, second value quantity added like:

[ ['a', 3], # since 'a' existed quantity added 1 + 2 becomes 3 ['b',2], ['c',6]   # 'c' becomes 1 + 5 = 6 ] 

how python ?

i'd suggest use collections.defaultdict() below:

from collections import defaultdict  l = [ ['a', 1], ['b',2], ['c',1], ['a', 2], ['c', 5] ]  d = defaultdict(int) key, value in l:     d[key] += value  print(d.items()) 

output:

dict_items([('b', 2), ('a', 3), ('c', 6)]) 

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also can use try...expect instead of collections.defaultdict()...if you'd like:

d = {} key, value in l:     try:         d[key] += value     except keyerror:         d[key] = value 

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also, can try if...else:

d = {} key, value in l:     if key in d:         d[key] += value     else:         d[key] = value