Slicing List items in python

Question

I have ordered list of string elements which I need to iterate.. starting from specific element/item from the list until the end.

The list that I have:

ip_list = ['input1','input2','input3',....,'input10']

I wanted to iterate from any given element (which would be dynamic on each run) for example consider input3 currently till the end of List.

So I wanted to achieve something like this:

for item in ip_list[input3:]:
    # my logic base

I have searched out that, in Python, we can slice the list with positional base but not on value base.

I'm not sure I understand the question. Can you show an example? — Aran-Fey, May 24 '18 at 08:32
Your question is very unclear and not specific to anything, you should show your data and your expected output, and stuff you already tried to do with it. Please provide a [Minimal, Complete, and Verifiable example](https://stackoverflow.com/help/mcve). — Ofer Sadan, May 24 '18 at 08:32
hope it help you. https://stackoverflow.com/questions/509211/understanding-pythons-slice-notation — rajini raja, May 24 '18 at 08:36

score 2 · Accepted Answer · answered May 24 '18 at 08:39

Yes using index() finds the position of an element in a list.

So if your list looks like this:

ip_list = ['input1','input2','input3']

And you want to initerate from input3 onward then using ip_list.index('input3') returns the position of input3 (so 2).

You then just have to slice the list in the normal way (as if you were doing ip_list[2:]) but using index():

for item in ip_list[ip_list.index('input3'):]:
    # my logic base

See Finding the index of an item given a list containing it in Python

score 1 · Answer 2 · answered May 24 '18 at 08:40

list[list.index(value):]

see https://docs.python.org/3/tutorial/datastructures.html

list.index(x[, start[, end]])

Return zero-based index in the list of the first item whose value is x. Raises a ValueError if there is no such item.

The optional arguments start and end are interpreted as in the slice notation and are used to limit the search to a particular subsequence of the list. The returned index is computed relative to the beginning of the full sequence rather than the start argument.

score 0 · Answer 3 · answered May 24 '18 at 08:52

Here's a solution based on iterators that works with any iterable, not just lists:

def iterate_from(iterable, start_value):
    # step 1: get an iterator
    itr = iter(iterable)

    # step 2: advance the iterator to the first matching value
    first_value = next(value for value in itr if value == start_value)

    # step 3: yield the remaining values
    yield first_value
    yield from itr

Here I used the iter function to get an iterator from the iterable, and the next function to move that iterator forward. You may also be interested in What does the "yield" keyword do?.

You would use it like this:

ip_list = ['input{}'.format(i) for i in range(1, 11)]

for ip in iterate_from(ip_list, 'input7'):
    print(ip)

# output:
# input7
# input8
# input9
# input10

score -1 · Answer 4 · edited Oct 11 '19 at 06:06

-1

ip_list = ['input{}'.format(i) for i in range(1,10)]
for item in ip_list[3:]:
    print(item)

edited Oct 11 '19 at 06:06

peterevans

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answered Oct 11 '19 at 03:20

Dipesh Chaudhary

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Slicing List items in python

4 Answers4