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Python | Insert value after each k letters in given list of string
• Last Updated : 20 May, 2019

Given a list of string, write a Python program to Insert some letter after each k letters in given list of strings.

As we know inserting element in a list is quite common, but sometimes we need to operate on list of strings by considering each letter and insert some repeated elements some fixed frequency. Let’s see how to achieve this task using Python.

Method #1: Using enumerate() method

 `# Python program to insert value after``# each k letters in given list of string``list1 ``=` `[``'p'``, ``'y'``, ``'t'``, ``'h'``, ``'o'``, ``'n'``] `` ` `# printing original list ``print` `(``"Original list : "` `+` `str``(list1)) `` ` `# initializing k ``k ``=` `'G'`` ` `# initializing N ``N ``=` `2`` ` `# using join() + enumerate() ``# inserting K after every Nth number ``output ``=` `list``(''.join(i ``+` `k ``*` `(N ``%` `2` `=``=` `1``) ``        ``for` `N, i ``in` `enumerate``(list1))) `` ` `# printing result ``print` `(``"The lists after insertion : "` `+` `str``(output)) `
Output:
```Original list : ['p', 'y', 't', 'h', 'o', 'n']
The lists after insertion : ['p', 'y', 'G', 't', 'h', 'G', 'o', 'n', 'G']
```

Method #2: Using itertools

 `# Python program to insert value after``# each k letters in given list of string``from` `itertools ``import` `chain `` ` `list1 ``=` `[``'p'``, ``'y'``, ``'t'``, ``'h'``, ``'o'``, ``'n'``] `` ` `# printing original list ``print` `(``"Original list : "` `+` `str``(list1)) `` ` `# initializing k  ``k ``=` `'x'``   ` `# initializing N ``N ``=` `3``   ` ` ` `# inserting K after every Nth number  ``output ``=` `list``(chain(``*``[list1[i : i ``+` `N] ``+` `[k]  ``              ``if` `len``(list1[i : i ``+` `N]) ``=``=` `N  ``else` `list1[i : i ``+` `N]  ``              ``for` `i ``in` `range``(``0``, ``len``(list1), N)])) `` ` `# printing result ``print` `(``"The lists after insertion : "` `+` `str``(output)) `
Output:
```Original list : ['p', 'y', 't', 'h', 'o', 'n']
The lists after insertion : ['p', 'y', 't', 'x', 'h', 'o', 'n', 'x']
```

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