Question

I’d like to make an if statement to detect if a string could be formed with items from lists, in order. For example, if I want to check if a term had the same meaning as “HelloWorld”, I’d have a “hello” list with ['hello', 'Hello', 'Hi', 'Greetings', 'Hola'], and a “world” list with ['world', 'World', 'Planet', 'Earth']. Then, check if a string is equal to any item from the “hello” list, directly followed by any item from the “world” list. “HelloWorld”, “GreetingsEarth”, and “HiPlanet” would all successfully trip the if statement. How would I do this? I’d like to use Python lists, so regex (a|b) seems impractical.

Answer 1

If you want to avoid a regular expression, you can use a generator expression that tests each combination (generated via itertools.product):

import itertools
combinations = (''.join((first, second)) for first, second in itertools.product(a, b))
any('HelloWorld' == combination for combination in combinations)

Note that this is far slower than the regular expression approach, especially when hitting the worst-case scenario (no match):

>>> timeit.timeit('search("HelloWorld"); search("HiThere")', 'from __main__ import reMatch as search')
1.8922290802001953
>>> timeit.timeit('search("HelloWorld"); search("HiThere")', 'from __main__ import genMatch as search')
18.3697190284729

The generator expression is 10 times slower than the regular expression approach.

(I used a re.compile() compiled regular expression for the test).