Combine elements of lists if some condition

Question

How do I combine the elements of a list if some condition is met.

I\'ve seen posts about combining elements of a list, but not with some condition.

Answer 1

Here's my solution:

words = [
    ['this','that!','riff','raff'],
    ['hip','hop!','flip!','flop'],
    ['humpty','dumpty!','professor!','grumpy!']
]

output = []
for wl in words:
    out_wl = []
    bang_wl = []
    for w in wl:
        if '!' in w:
            bang_wl.append(w)
        else:
            if bang_wl:
                out_wl.append(','.join(bang_wl))
                bang_wl = []
            out_wl.append(w)
    if bang_wl:
        out_wl.append(','.join(bang_wl))
    output.append(out_wl)

print output

Output:

[['this', 'that!', 'riff', 'raff'], ['hip', 'hop!,flip!', 'flop'], ['humpty', 'dumpty!,professor!,grumpy!']]

bang_wl accumulates words with ! until it hits a word that doesn't contain a !. At this point, it joins the words in bang_wl and appends to the output_wl list.