list.extend and list comprehension
When I need to add several identical items to the list I use list.extend:
a = ['a', 'b', 'c']
a.extend(['d']*3)
Result
['a', 'b', 'c', 'd', 'd', 'd']
But, how to do the similar with list comprehension?
a = [['a',2], ['b',2], ['c',1]]
[[x[0]]*x[1] for x in a]
Result
[['a', 'a'], ['b', 'b'], ['c']]
But I need this one
['a', 'a', 'b', 'b', 'c']
Any ideas?
Stacked LCs.
[y for x in a for y in [x[0]] * x[1]]
An itertools approach:
import itertools
def flatten(it):
return itertools.chain.from_iterable(it)
pairs = [['a',2], ['b',2], ['c',1]]
flatten(itertools.repeat(item, times) for (item, times) in pairs)
# ['a', 'a', 'b', 'b', 'c']