Change Boolean Value Python 3

Question

I'm trying to write a code that takes a Boolean value and swaps it for the opposite in a list. So let's say I start out with 100 Falses and want to change every one to True. Then I want to change every other one to False, starting at the second one. I hope that makes sense.

an example would be:

>>>False False False False False False False False False False
>>>True True True True True True True True True True
>>>True False True False True False True False True False
>>>True False False False True True True False False True

`python generators` http://stackoverflow.com/questions/102535/what-can-you-use-python-generator-functions-for — user2485710, Nov 13 '13 at 05:31
What operation is done for the third one to get the fourth? (`True False False False True True True True False True`) — falsetru, Nov 13 '13 at 05:45
@WhooCares, Now it change items at indexes of 2, 5, 8, 9.. (3rd, 6th, 9th, 10th) I still don't get it what change rule is applied. — falsetru, Nov 13 '13 at 06:26

score 1 · Accepted Answer · answered Nov 13 '13 at 05:44

1

Using list comprehension and slicing:

>>> lst = [False] * 10
>>> lst
[False, False, False, False, False, False, False, False, False, False]
>>> lst[:] = [not x for x in lst]
>>> lst
[True, True, True, True, True, True, True, True, True, True]
>>> lst[1::2] = [not x for x in lst[1::2]]
>>> lst
[True, False, True, False, True, False, True, False, True, False]

answered Nov 13 '13 at 05:44

falsetru

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How would you do this for large numbers? Say 100? Or 100? – Whoo Cares Nov 13 '13 at 06:20
@WhooCares, This code should work without modification. (except the first `lst = [False] * 10`. – falsetru Nov 13 '13 at 06:23
@WhooCares, If it is really huge, you can use generation expression instead of list comprehension: `lst[1::2] = (not x for x in lst[1::2])` – falsetru Nov 13 '13 at 06:24

JoelWilson · Answer 2 · 2013-11-13T06:36:49.513

0

Switch every other element to its opposite:

my_list = [False, False, False, False, False, False, False]
for index in range(0, len(my_list), 2):
    my_list[index] = not my_list[index]

edited Nov 13 '13 at 06:36

answered Nov 13 '13 at 05:45

JoelWilson

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Fixed it - renamed list[index] to my_list[index]. – JoelWilson Nov 13 '13 at 06:24
Using `range(0, len(my_list), 2)`, you don't need to use `if`. – falsetru Nov 13 '13 at 06:33

Change Boolean Value Python 3

2 Answers2