How can I unite some elems in the list?

[Larz60+]

here's one way:

list_ = ['did', 'is', 'not', 'come', 'will', 'kill', 'are', 'not']

newitem = ''
for n, item in enumerate(list_):
   if item == 'not' and n > 0:
       newitem = newitem + ' ' + list_[n-1]
print(newitem)

results:

Output:
is are

A better way would be to use a list comprehension