How to Substring a String in Python?

In Python, the string is a sequence of Unicode characters, represented within the single or double quotes. A string can contain any character, including alphanumeric and special symbols. In this tutorial, we will learn how to extract a substring from a string in Python. Also, we will know the different methods that we can use to extract a substring from a string.

What is a Substring in Python?

A substring is a sequential part of a string. If a string a is present in a string b , then string a would be considered as a sub-string of b. Also, in Python, this substring is also referred to as a Python string slicing .

String Slicing in Python

In Python, to access a string, we use the variable name of the string. By only using the variable name, we can get the complete string, but if we want to retrieve a part or a specific character from the string, then we use indexing and slicing. In slicing, we use index values of a given string to grab a sequence of characters from the string.

sub_string = string[ strartIndex : endIndex]

Note : The index value starts from 0.

Code Example

string = "Hello World It's TechGeekBuzz"

sub_string_1 = string[0:5]

print("The Sub String 1 is:", sub_string_1)

print("The Sub String 2 is:", sub_string_2)

Output

The Sub String 1 is: Hello
The Sub String 2 is: World It's TechGeekBuzz 

More Examples on Python Sub Strings

1. Slice a Python String Without Using the End Index String[StartIndex:]

If we do not specify the end index value, then it would be treated as the last index value. Code Example

string = "hello world techgeekbuzz"

sub_string = string[5:]

print(sub_string)

Output

world techgeekbuzz 

2) Slice a Python String Without Specifying the Starting Index String[:EndIndex]

If we do not specify the starting index while slicing the string, then the starting index becomes 0 by default.

Code Example

string = "hello world techgeekbuzz"
sub_string = string[:5]
print(sub_string)

Output

hello

3. Slice a Python String Without Specifying the Starting and Ending Index Values string[:]

If we do not specify the starting and ending index values for the slicing, then the slicing operation returns the complete string from index value 0 to (n-1), where n is the length of the string.

Code Example

string = "hello world techgeekbuzz"
sub_string = string[:]
print(sub_string)

Output

hello world techgeekbuzz

4. String Slicing With Steps

By far, we only discussed how we could specify the starting and ending index values during slicing to get a substring. But slicing also supports step value, which describes in what sequence the substring should be retrieved from a string, and the step value is the last part of the slicing.

Syntax

slice = string[ startIndex: endIndex: steps]

< Note >: By default, the step value is 1, which signifies that the step count should be +1 from the starting index to the end index. And its value could be any integer number except 0.

5. Slice a Python Sting with Step Count 2

If the step value is 2, then the string slice will skip every consecutive value and grab the alternative one.

Code Example

string = "hello world techgeekbuzz"
slice = string[::2]
print(slice)

Output

hlowrdtcgebz

6. Reverse a String Using Slicing in Python

A string can be reversed using slicing in Python . By setting the step value to -1 and leaving the startIndex and endIndex blank, the string will be reversed. The -1 represents that the count should be negative and 1 step at a time.

Code Example

>>>string = "hello world techgeekbuzz"
>>> reverse = string[ : : -1]
>>> print(reverse)
zzubkeeghcet dlrow olleh

Find All The Possible Substrings of a String in Python

To find all the possible substrings of a string in Python, we have to create a nested for loop.

Code Example

string ="python"

all_sub_strings =set()

for i in range(len(string)):
    for j in range(i, len(string)):
        all_sub_strings.add(string[i:j])
print(all_sub_strings)

Output

{'', 'yt', 'ytho', 'y', 'yth', 't', 'ho', 'pytho', 'o', 'pyt', 'pyth', 'p', 'py', 'th', 'h', 'tho'}

< Note >: An empty string is also a substring.

Find All the Possible Substrings of a String in Python using List Comprehension

Python list comprehension provides an alternative to creating a list of elements using for loop within a single line. Here is an example of finding all the possible substrings of a string using list comprehension. Code Example

string = "python"
sub_strings = [string[i:j] for i in range(len(string)) for j in range(i,len(string))]
print(set(sub_strings))

Output

{'pytho', 'pyt', 'ytho', 'y', 'tho', 'th', 't', 'pyth', 'h', 'yt', 'yth', 'py', 'p', 'ho', 'o', ''}

How to Check If a String is a Substring?

To check if a string is a substring of another string, we can use the in operator. The Python operator checks if the string is a substring and returns True. Else, it returns False.

Code Example

string = "python"
>>> "p" in string
True
>>> "pytho" in string
True
>>> "" in string
True
>>> "on" in string
True
>>> "hell" in string
False

Summary

In this tutorial, you learned all about how to substring a string in python. You also learned how to find all the possible substrings for a string and how to check if a string is a substring or not using the in operator. A substring in Python is also known as string slicing, and most of the time, you will be hearing and using the word slicing.

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