在每 2 个元素之后在列表中插入元素

Question

I have this code:

l = [1.0, 2.0, 3.0, 4.0, 5.0, 6.0]

def add(l, n):
    lret = l.copy()
    i = n
    while i <= len(lret):
      lret.insert(i, 0.0)
      i += (n+1)
    return lret

lret = add(l,2)

print(lret)

Is a way to make the add() function a one-line function?

Answer 1

You can use zip() to build tuples that contain n elements from the original list with an added element, and then use chain.from_iterable() to flatten those tuples into the final list:

from itertools import repeat, chain
def add(lst, n):
    return list(chain.from_iterable(zip(*(lst[s::n] for s in range(n)), repeat(0.0))))

This outputs:

[1.0, 2.0, 0.0, 3.0, 4.0, 0.0, 5.0, 6.0, 0.0]

Answer 2

Possible solution if you want the whole block in one line:

return [x for y in (l[i:i + n] + [0.0] * (i < len(l) - n + 2) for
                   i in xrange(0, len(l), n)) for x in y]

Gives the same output

[1.0, 2.0, 0.0, 3.0, 4.0, 0.0, 5.0, 6.0, 0.0]

Answer 3

Found another way to do it:

def add(l,n=2):
    return [item for sublist in [(e,) if i % n == 0 or i == 0 else (e, 0.0) for i, e in enumerate(l)] for item in sublist]

[1.0, 2.0, 0.0, 3.0, 4.0, 0.0, 5.0, 6.0, 0.0]