AppDividend
Latest Code Tutorials

Python Slicing: How to Slice List or Sequence using slice()

Slicing an object in Python is means to slice the given sequences like string, bytes, tuple, list, range, or any object which supports the sequence protocol ( which implements __getitem__() and __len__() method).

Python Slicing

Python slice() is an inbuilt function that creates the slice object representing the set of indices specified by range(start, stop, step). The slice object is used to determine how to slice the sequence.

You can specify where to start the slicing and where to end.  You can also determine the step, which allows you to, e.g., slice only every other item.

Syntax

The syntax of the Python slice() function is the following.

slice(stop)
slice(start, stop, step)

Parameters

The start parameter is optional, and it is the starting integer where the slicing of the object starts.

The stop parameter is required, and it is an integer number specifying at which position to end the slicing.

The step parameter is optional, and it is an integer value that determines the increment between each index for slicing.

Let’s see the example of the Python slice() method.

# app.py

A = ('Bad Bunny', 'Louis Fonsi', 'Daddy Yankee', 'Drake')
result = slice(1,3)
print(A[result])

The output of the above program is following.

Python Slice Example | slice() Method Tutorial

See in the above example, we have sliced the object from the index 1 to 3, and we get the elements like Louis Fonsi and Daddy Yankee.

Get substring from a given string using a slice object.

Let’s see the following example of String, where we will get a substring from a string.

# app.py

A = 'AppDividend'
result = slice(3)
print(A[result])

Now, see the output below.

Get substring from a given string using slice object

Slice String Using Negative Index

In the following example, we will slice a string based on the negative index.

# app.py

A = 'AppDividend'
result = slice(-3, -1)
print(A[result])

In the below example, we have passed the negative index, which means that the execution starts from the end and then goes forward and returns the value.

See the output below.

Slice String Using Negative Index

Python slicing array

To slice an array in Python, use the numpy library. The np.array() function creates an array, and you can slice an array by taking elements from one given index to another given index.

You can pass the slice instead of an index like this: [start: end].

You can also define the step like this: [start: end: step].

If you don’t pass the start parameter, it’s considered 0.

If you don’t pass the end argument, it’s considered the size of an array in that dimension.

If you don’t pass the step parameter, it’s considered 1.

# app.py

import numpy as np

arr = np.array([1, 2, 3, 4, 5, 6, 7, 8])

print(arr[2:7])

Output

[3 4 5 6 7]

In this example, we are slicing an array from index 2 to 7. Here, one thing to remember that 2nd index value is not included in the final output, but the last index, which is 7, will be included in the output. That means, start index won’t be included, but the end index will be included.

Slicing 2D Arrays in Python

The syntax for slicing 2D arrays in Python is the following.

<slice> = [start_row:end_row, start_col:end_col]

Let’s slice a 2D array.

# app.py

import numpy as np

arr = np.array([[1, 3, 5, 7], [2, 4, 6, 8]])
print(arr)
b = arr[0:2, 0:3]
print(b)

Output

[[1 3 5 7]
 [2 4 6 8]]
[[1 3 5]
 [2 4 6]]

Finally, Python Slicing Example is over.

Leave A Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.