Просто тренируюсь ...
def word_counter(passlist):
do_count = lambda x: len(x.split())
result=[]
for elem in passlist:
if isinstance(elem, list):
result += [word_counter(elem)]
elif isinstance(elem, str):
result += [do_count(elem)]
return result
print(word_counter([['We test robots'], ['Give us a try'], [' ']]))
# output: [[3], [4], [0]]
print(word_counter(['First of all', ['One more test'], [['Trying different list levels'], [' ']], 'Something more here']))
# output: [3, [3], [[4], [0]], 3]