Python – Converts a list with 1 comma-separated string to a two-dimensional list

I don’t know much about python’s map/reduce function, but is there a way to convert this input list to a given output?

inp  = [1,2,3,"a,b,c",4,"blah"]
outp = [
    [1,2,3,'a',4,'blah'],
    [1,2,3,'b',4,'blah'],
    [1,2,3,'c',4,'blah']
    ]

So far, I’ve only done this by using loops, and it doesn’t look like an effective approach :

inp[3]=inp[3].split(',')
out=[]
for i in inp[3]:
    k=list(inp)
    k[3]=i
    out.append(k)   

Given the hard constraints, you can speed up using list understanding and slicing to make it cleaner a bit:

inp = [1, 2, 3, "a,b,c", 4, "blah"]
outp = [inp[:3] + [i] + inp[4:] for i in inp[3].split(",")]
# [[1, 2, 3, 'a', 4, 'blah'],
#  [1, 2, 3, 'b', 4, 'blah'],
#  [1, 2, 3, 'c', 4, 'blah']]

But it doesn’t reduce complexity. In fact, for your example, it may run slower than your method because it must perform 3 list creations and a list join for each entry in inp[3], unless inp[3] is long and list understanding does not show its real advantage of offsetting list creation overhead.