Python List with First N Elements

Get Python List with First N Elements

There are many ways to get given Python List with first N elements.

You can use slicing to slice the given list and get a new list with the first N elements of the original or source list.

Or, you can access the list using index, and use a looping statement like for loop to get the first N elements.

Another way would be to use list comprehension. This is an overkill to get the first N elements, but would be educative to learn Python programming.

So, based on the requirement, you may choose one of the above approaches to get or create a new list with the first N elements from the source list.

1. List with First N Elements using Slicing

The syntax to get the list with first N elements using slicing is

new_list = source_list[:N]

The source list is not modified. A new list is created with the first N elements of source list.

Following is an example program, where we initialize a list, and copy the first N elements of the list to a new list using slicing.

source_list = [8, 4, 7, 3, 6, 1, 9]
N = 4
new_list = source_list[:N]
print(source_list)
print(new_list)

Output

[8, 4, 7, 3, 6, 1, 9]
[8, 4, 7, 3]

The new list contains first 4 elements of source list.

2. List with First N Elements using For Loop

To get the first N elements of a list, use for loop with range(0, N), create a new empty list, and append the elements of source list to new list in the for loop.

range(0, N) iterates from 0 to N-1, insteps of 1. N is not included.

list.append(element) appends given element to the list.

Following is an example program, where we initialize a list, and use for loop to get the first N elements of the given list.

source_list = [8, 4, 7, 3, 6, 1, 9]
N = 4
new_list = []
for index in range(0, N):
    new_list.append(source_list[index])
print(source_list)
print(new_list)

Output

[8, 4, 7, 3, 6, 1, 9]
[8, 4, 7, 3]

3. List with First N Elements using List Comprehension

In the following program, we use list comprehension with if condition and collect those items of source list whose index is less than N.

source_list = [8, 4, 7, 3, 6, 1, 9]
N = 4
new_list = [x for index, x in enumerate(source_list) if index < N]
print(source_list)
print(new_list)

Output

[8, 4, 7, 3, 6, 1, 9]
[8, 4, 7, 3]

Summary

In this tutorial of Python Examples, we learned how to get the list without its last element, with the help of slicing and pop() method.