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Python | Incremental slice partition in list
• Last Updated : 27 Aug, 2019

Sometimes, while working with lists, we can come across a problem in which we need to slice a list incrementally, i.e, with each slice, number of elements increase by 1. This has application in competitive programming. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using loops
This is the brute force method by which this task can be performed. We just manually count and increase the counter with each iteration for slicing and dictionary key creation.

 `# Python3 code to demonstrate working of``# Incremental slice partition in list``# Using loop`` ` `# initializing list``test_list ``=` `[``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``, ``8``, ``9``, ``10``]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# Incremental slice partition in list``# Using loop``res ``=` `{}``N ``=` `1``strt ``=` `0``while` `strt < ``len``(test_list):``    ``res[N] ``=` `test_list[strt : strt ``+` `N]``    ``strt ``+``=` `N``    ``N ``+``=` `1`` ` `# printing result ``print``(``"The partitioned dictionary from list is : "` `+` `str``(res))`
Output :

The original list is : [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
The partitioned dictionary from list is : {1: , 2: [2, 3], 3: [4, 5, 6], 4: [7, 8, 9, 10]}

Method #2 : Using `enumerate() + slice() + next() + iter() + count()`
The combination of above functions can be used to perform this task. In this, `next()` is used to iterate the list converted to iterator by `iter()`. The `slice()` performs list slicing. The count() helps in managing the counter and enumerate keeps track of element and indices in list.

 `# Python3 code to demonstrate working of``# Incremental slice partition in list``# Using enumerate() + slice() + next() + iter() + count()``from` `itertools ``import` `islice, count`` ` `# initializing list``test_list ``=` `[``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``, ``8``, ``9``, ``10``]`` ` `# printing original list``print``(``"The original list is : "` `+` `str``(test_list))`` ` `# Incremental slice partition in list``# Using enumerate() + slice() + next() + iter() + count()``res ``=` `{key : val ``for` `key, val ``in` `enumerate``(``iter``(``lambda` `i ``=` `iter``(test_list),``                          ``c ``=` `count(``1``): ``list``(islice(i, ``next``(c))), []), ``1``)}`` ` `# printing result ``print``(``"The partitioned dictionary from list is : "` `+` `str``(res))`
Output :

The original list is : [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
The partitioned dictionary from list is : {1: , 2: [2, 3], 3: [4, 5, 6], 4: [7, 8, 9, 10]}

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