search.py

words = ['abc', 'ubuntu', 'linux', 'ubuntu 16 LTS', 'redhat', 'unix', 'windows', 'macos X']

def tre(w):
    w = w.lower()
    r = {'__' + w[0], '_' + w[:2]}
    for i in range(len(w)):
        k = w[i:i+3]
        while len(k) < 3:
            k += '_'
        r.add(k)
    
    return r

result = []
h = tre('ubuXntu16LTS')
for w in words:
    result.append((len(tre(w) & h), w))

for w in sorted(result, reverse=True):
    print(w)

(7, 'ubuntu 16 LTS')
(4, 'ubuntu')
(1, 'windows')
(1, 'unix')
(0, 'redhat')
(0, 'macos X')
(0, 'linux')
(0, 'abc')