python - que - list.extend y lista de comprensión

python extend expand

Question

Cuando necesito agregar varios elementos idénticos a la lista, uso list.extend:

a = [''a'', ''b'', ''c'']
a.extend([''d'']*3)

Resultado

[''a'', ''b'', ''c'', ''d'', ''d'', ''d'']

Pero, ¿cómo hacer lo similar con la lista de comprensión?

a = [[''a'',2], [''b'',2], [''c'',1]]
[[x[0]]*x[1] for x in a]

Resultado

[[''a'', ''a''], [''b'', ''b''], [''c'']]

Pero necesito este

[''a'', ''a'', ''b'', ''b'', ''c'']

¿Algunas ideas?

Answer 1

LCs apilados.

[y for x in a for y in [x[0]] * x[1]]

Answer 2

Si prefieres ampliar sobre las comprensiones de la lista:

a = []
for x, y in l:
    a.extend([x]*y)

Answer 3

Un enfoque de itertools :

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'']

Answer 4

import operator
a = [[''a'',2], [''b'',2], [''c'',1]]
nums = [[x[0]]*x[1] for x in a]
nums = reduce(operator.add, nums)

Answer 5

>>> a = [[''a'',2], [''b'',2], [''c'',1]]
>>> [i for i, n in a for k in range(n)]
[''a'', ''a'', ''b'', ''b'', ''c'']

Answer 6

>>> a = [[''a'',2], [''b'',2], [''c'',1]]
>>> sum([[item]*count for item,count in a],[])
[''a'', ''a'', ''b'', ''b'', ''c'']