Useful list-indexing trick
Hi all,
I just found this while googling, and it sort of blew my mind. I'm writing in Python, but I guess you could use this in any language.
So if you've got a list of items you want to cycle through, it's obvious to go:
current_index += 1
if current_index >= len(l):
current_index -= len(l)
elif current_index < 0: # We can probably scroll back too.
current_index += len(l)
# Do stuff.Seems there is a quicker way, which seems to be foolproof, as well as a 1-liner:
current_index = (current_index + 1) % len(l)
# Do stuffThis works because the % operator does modulus, which is to say it returns the remainder of trying to shove the number on the left into the number on the right: 10 % 3 is 1, because 3's into 10 go a maximum of 3 times, with 1 left over.
Back to lists, given the listlike:
>>> l = ['first item', 'second item', 'third item']
>>> l[0 % len(l)]
'first item'
>>> l[1 % len(l)]
'second item'
>>> l[2 % len(l)]
'third item'
>>> l[3 % len(l)]
'first item'
>>> l[-1 % len(l)]
'third item'
>>> l[-2 % len(l)]
'second item'My world has officially been rocked.
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