Generate all substring

substring.py

def generate_substring(s):
    t = [s, ]
    for i in list(s):
        if i not in t:
            t.append(i)
            
        for j in t:
            if j.find(i) >= 0:
                continue
            x = i + j if i < j else j + i
            if len(x) <= len(s) - 1 and x not in t:
                t.append(x)
    return t

# Example:
print(generate_substring("abcd"))
# Result:
['abcd', 'a', 'b', 'ab', 'c', 'ac', 'bc', 'abc', 'd', 'ad', 'bd', 'abd', 'cd', 'acd', 'bcd']