Generate all possible substrings in sequence

Question

I'm searching for a library or an efficient way to implement the following in Python

Input: 
"He was hungry"

Desired Output:
[["He","was","hungry"]
["He was","hungry"]
["He","was hungry"]
["He was hungry"]]

Answer 1

def f(a):
    if(len(a) == 0):
        yield []
    for i in range(len(a)):
        for c in f(a[i+1:]):
            yield [" ".join(a[:i+1]), *c]


s = "He was hungry"
print(list(f(s.split())))

[['He', 'was', 'hungry'], ['He', 'was hungry'], ['He was', 'hungry'], ['He was hungry']]