Split array based on value

In one line:

[list(g) for k, g in itertools.groupby(foo, lambda x: x == '') if not k]

Edit:

From the oficial documentation:

groupby

generates a break or new group every time the value of the key function changes (which is why it is usually necessary to have sorted the data using the same key function).

The key I generate can be True, or False. It changes each time we find the empty string element. So when it's True, g will contain an iterable with all the element before finding an empty string. So I convert this iterable as a list, and of course I add the group only when the key change

Don't know how to explain it better, sorry :/ Hope it helped

Create a list containing a single list.

output = [[]]

Now, iterate over your input list. If the item is not '', append it to the last element of output. If it is, add an empty list to output.

for item in foo:
    if item == '':
        output.append([])
    else:
        output[-1].append(item)

At the end of this, you have your desired output

[['1', '2'], ['1', '2', '3'], ['1'], ['2']]