The only improvement I could think of is, to use list comprehension like this
def get_all_substrings(input_string):
length = len(input_string)
return [input_string[i:j+1] for i in xrange(length) for j in xrange(i,length)]
print get_all_substrings('abcde')
The timing comparison between, yours and mine
def get_all_substrings(string):
length = len(string)
alist = []
for i in xrange(length):
for j in xrange(i,length):
alist.append(string[i:j + 1])
return alist
def get_all_substrings_1(input_string):
length = len(input_string)
return [input_string[i:j + 1] for i in xrange(length) for j in xrange(i,length)]
from timeit import timeit
print timeit("get_all_substrings('abcde')", "from __main__ import get_all_substrings")
# 3.33308315277
print timeit("get_all_substrings_1('abcde')", "from __main__ import get_all_substrings_1")
# 2.67816185951
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