[Tut] Python Slice Remove First and Last Element from a List

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Python Slice Remove First and Last Element from a List

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Problem Formulation

Question: Given a Python list stored in a variable

Code:

lst

. How to remove the first and last elements from the list

Code:

lst

?

Example: The list

Code:

['Alice', 'Bob', 'Carl', 'Dave']

stored in variable

Code:

lst

becomes

Code:

['Bob', 'Carl']

.

Method 1: Slicing List[1:-1]

To remove the first and last elements from a Python list, use the expression

Code:

lst = lst[1:-1]

that uses a Python feature called slicing with the syntax

Code:

variable[start:stop]

to iterate over a sequence starting from the

Code:

start

index (included) and ending in the element at

Code:

stop

index (excluded). If

Code:

stop

is a negative integer such as

Code:

-i

, Python takes the i-th right-most element.

Here’s an example:

Code:

lst = ['Alice', 'Bob', 'Carl', 'Dave'] lst = lst[1:-1] print(lst) # ['Bob', 'Carl']

This code snippet removes the first element

Code:

'Alice'

and the last element

Code:

'Dave'

from the list.

Note that this approach also works for lists with one element:

Code:

lst = ['Alice'] lst = lst[1:-1] print(lst) # []

… and also for an empty list with zero elements:

Code:

lst = [] lst = lst[1:-1] print(lst) # []

Feel free to get some background on slicing by watching the following tutorial:



Learn More: An Introduction to Python Slicing

Method 2: Slicing List Without Negative Index

To remove the first and last elements from a Python list, you can also use the slightly more complex expression

Code:

lst = lst[1:len(lst)-1]

that assigns the result of the slicing operation to the list and, thereby, overwrites the original longer list. We decrement the

Code:

len()

function result to obtain the index of the last element that is excluded from the slice.

Here’s an example:

Code:

lst = ['Alice', 'Bob', 'Carl', 'Dave'] lst = lst[1:len(lst)-1] print(lst) # ['Bob', 'Carl']

You can watch my related tutorial video:



Learn More: The Python

Code:

len()

function

Method 3: list.pop() and list.pop(0)

To remove the first element of a Python list, you can use the

Code:

list.pop(0)

method. To remove the last element of a Python list, you can use the

Code:

list.pop()

method without argument. You can call both to remove the first and the last elements if the list has at least two elements.

Here’s a minimal example:

Code:

lst = ['Alice', 'Bob', 'Carl', 'Dave'] lst.pop() # remove last lst.pop(0) # remove first print(lst) # ['Bob', 'Carl']

However, for a list with less than two elements, this will raise an

Code:

IndexError: pop from empty list

. A simple

Code:

if

check can make sure that the list has at least two elements—and otherwise simply override it with the empty list.

Here’s some background info in case you want to dive deeper into this approach:

The

Code:

list.pop()

method removes and returns the last element from an existing

Code:

list

. The

Code:

list.pop(index)

method with the optional argument

Code:

index

removes and returns the element at the position

Code:

index

.



Learn More: The Python

Code:

list.pop()

method

Summary

You’ve learned the three easy ways to remove both the first and last elements from a Python list:

• Method 1: Slicing
  Code:

  list[1:-1]
  
  
• Method 2: Slicing List Without Negative Index
  Code:

  list[1:len(list)-1]
  
  
• Method 3:
  Code:

  list.pop()
  and
  Code:

  list.pop(0)

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