# Python | List Initialization with alternate 0s and 1s

• Last Updated : 25 Nov, 2022

The initialization of a list with a single number is a generic problem whose solution has been dealt with many times. But sometimes we require to initialize the list with elements alternatively repeating K no. of times. This has use cases in M.L. or A. I algorithms that require presetting of data in lists. Let’s discuss certain ways in which this problem is solved.

Method #1: Using list comprehension In this method, we insert elements in the list alternatively for the specific number of times of each element’s occurrence. It takes the remainder of the sum of counts of both occurrences of elements with the particular occurrence of elements for cycle computation.

## Python3

 `# Python3 code to demonstrate``# to perform cyclic initialization``# using list comprehension` `# count of 1``count_1 ``=` `4` `# count of 0``count_0 ``=` `3` `# total length of list``size ``=` `14` `# initializing list cyclically``# using list comprehension``test_list ``=` `[``1` `if` `i ``%` `(count_1 ``+` `count_0) < count_1``             ``else` `0` `for` `i ``in` `range``(size)]` `# printing list after change``print``(``"The list after initializing : "` `+` `str``(test_list))`

Output

```The list after initializing : [1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0]
```

Method #2 : Using itertools.cycle() + itertools.islice() This is the most pythonic way in which we can perform the cyclic initialization. Slice each of the part of list into the allotted element size in a cyclic manner using cycle function.

## Python3

 `# Python3 code to demonstrate``# to perform cyclic initialization``# using itertools.cycle() + itertools.islice()``import` `itertools` `# count of 1``count_1 ``=` `4` `# count of 0``count_0 ``=` `3` `# total length of list``size ``=` `16` `# getting pattern``pattern ``=` `[``1``] ``*` `count_1 ``+` `[``0``] ``*` `count_0` `# initializing list cyclically``# using itertools.cycle() + itertools.islice()``test_list ``=` `list``(itertools.islice(itertools.cycle(pattern), size))` `# printing list after change``print``(``"The list after initializing : "` `+` `str``(test_list))`

Output

```The list after initializing : [1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 1]
```

Method #3 : Using *,extend() and slicing

## Python3

 `# Python3 code to demonstrate``# to perform cyclic initialization``# using list comprehension` `# count of 1``count_1 ``=` `4` `# count of 0``count_0 ``=` `3` `# total length of list``size ``=` `14` `# initializing list cyclically``x ``=` `[``1``]``*``count_1``y ``=` `[``0``]``*``count_0``res ``=` `[]``while``(``len``(res) <``=` `size):``    ``res.extend(x)``    ``res.extend(y)``res ``=` `res[:size]``# printing list after change``print``(``"The list after initializing : "` `+` `str``(res))`

Output

```The list after initializing : [1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0]
```

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