Substring in Python

Introduction

A part or a section of a string that can be separated from the main string is referred to as a substring. For instance,'stand' is a substring of 'understand'. The required substring is selected from the main string, which is declared in the program, using the slicing operation in Python. The syntax for substring in Python is as follows: string_var[start_index: end_index], where start and end index values represent the string's character place count and string_var is the variable used to declare a string value.

Overview

A string is a collection of Unicode characters. It consists of a series of characters, including alphanumeric and special characters. This article focuses on the Python substring concept and its operation.

What is a Substring?

Substrings are essentially a component of a string. To illustrate a section of string and perform some action on it, let's use an example.

Code:

statement = "Coding in Python is fun." 
substring = statement[0:7] 
print("Original Text :",statement) 
print("Substring :",substring)

Output:

Original Text: Coding in Python is fun.
Substring: Coding 

How to Create a Substring

Python provides different ways and styles to induce a substring, to check if a substring is present, to get the indicator of a substring, and more.

You can extract substring from string Python by slicing with indicators that get your substring as follows:

string [start.stop.step]

start- The starting indicator of the substring.

stop- The final indicator of a substring.

step- A number which is specifying the step of the slicing. The dereliction value is 1.

Both positive and negative numbers can be used as indices. The positive indices move from the beginning of the string to its end, while the negative indices move from the string's end to its beginning.

You will discover several Python operations related to substrings in this article.

How to Check if the Substring Is Found

In Python, one of the most common operations is checking a substring. Python uses a variety of methods, such as find(), index(), count(), etc., to determine whether a string contains a substring. The "in" operator, which is used as a comparison operator, is the fastest and most effective technique. Here, we'll discuss various strategies:

• Using an if-else statement, you can determine whether a Python substring is present in a string in Python. Depending on whether a condition is true or false, you can conditionally execute different blocks of code using the if-else statement.

# Take input from users 
MyString1 = "A buddy is obviously a geek indeed"
if "need" in MyString1: 
    print("Yes! it is present in this string") 
else: 
    print("No! it is not present") 

Output:

Yes! It is present in this string.

• using split() to determine whether a python substring is present in a string. Using the if condition, determine whether or not a substring is present in the given string after first breaking the given string into words and storing them in a variable.

# input strings str1 and substr 
string = "MMA is good" # or string=input() -> taking input from the user 
substring = "good" # or substring=input() 
# splitting words in a given string 
s = string.split() 
# checking condition 
# if substring is present in the given string then it gives output as yes 
if substring in s: 
    print("yes") 
else: 
    print("no")

Output:

Yes

• We can iteratively check each word, but Python has a built-in function called find() that performs a one-line check to see if a substring is present in the string. This issue can be resolved using the find() function, which returns -1 if it cannot be found and the first occurrence otherwise.

def check(string, sub_str): 
    if (string.find(sub_str) == -1): 
        print("NO") 
    else: 
        print("YES") 
# driver code 
string = "friends are good"
sub_str = "friends"
check(string, sub_str) 

Output:

Yes

• The Python count() method can be used to count the instances of a particular substring within a string. "Yes" will print if the substring is not found; otherwise, "no" will be printed.

def check(s2, s1): 
    if (s2.count(s1) > 0): 
        print("YES") 
    else: 
        print("NO") 
s2 = "A friend is a friend soulmate"
s1 = "friends"
check(s2, s1) 

Output:

No

Using a lambda function, check a Python substring between two characters in a string. A lambda function can be used to quickly check if a substring is present in any of the words in a string.

s="Like is Like"
s2="Like"
x=list(filter(lambda x: (s2 in s),s.split())) 
print(["yes" if x else "no"]) 

Output:

['Yes']

• Using regular expressions, you can determine whether a Python substring is present in a string in Python. You can define intricate search patterns for substring matching thanks to the strong pattern matching capabilities offered by regular expressions. Here's how to check for a substring in a string using regular expressions.

import re 
MyString1 = "A bro is helping hand and bro is a pure soul"
if re.search("need", MyString1): 
    print("Yes! it is present in the string") 
else: 
    print("No! it is not present") 

Output:

Yes! it is present in the string

How to Get the Substring From a Given String Using List Slicing

Here’s how you can get the substring from a given string using list slicing:

• Step size of 1 (no skipping): With this method, each character in the string's designated range is chosen.
• Step size of 2 (select every other item): With this method, every other character in the string's specified range is chosen.
• Step size of 3 (select every third item): With this strategy, every third character in the string within the designated range is chosen.
• Step size of -1 (reverse order): This method picks every character in reverse order from the string's specified range.
• Step size of -2 (reverse order, select every other item): With this method, every other character in the string's specified range is chosen in reverse order.
• Step size of -3 (reverse order, select every third item): With this method, every third character in the string's specified range is chosen in reverse order.

# Example 1: Get the first 3 characters of a string

myString = "Hello World"
substring = myString[0:3]
print(substring) # Output: "Hel"

# Example 2: Get each other character in a string

myString = "abcdefghijklmnopqrstuvwxyz"
substring = myString[0:len(myString):2]
print(substring) # Output: "acegikmoqsuwy"

# Example 3: Get a substring starting from the 4th position character and skipping every third character

myString = "abcdefghijklmnopqrstuvwxyz"
substring = myString[3:len(myString):3]
print(substring) # Output: "dgljmpsvy"

Output:

Hel acegikmoqsuwy dgjmpsvy

• List slicing has an O(stop-start) time complexity and an O(stop-start) space complexity when the step size is 1 (i.e., no skipping). This is because it generates a new list containing the sliced elements.
• Since list slicing only generates a new list containing the chosen elements when the step size is much greater than 1, the time complexity of the list slicing depends on the Python get all substring of length k of sliced substring.
• Due to the fact that only a portion of the original elements are added to the new list, the space complexity is O(stop-start/step).
• You can slice the Python string length in reverse order by using a negative step size. The complexity in terms of time and space is identical to that for positive step sizes.

Syntax of List Slicing

List slicing is a common practice in Python and is the most popular method used by programmers to solve practical problems. Consider a Python list. You must slice a list in order to access a specific subset of its elements. Use of the straightforward slicing operator, colon(:), is one way to accomplish this. With the help of this operator, one can specify the step as well as the starting and ending points for the slicing. From the original list, list slicing produces a new list.

List slicing in Python uses the following format:

Lst[ Initial : End : IndexJump ]

The indexing operators [and] can be used to quickly cut a string, as shown below:

string = 'dheaxkalmlprloeob'
string[2:15:2
'example'

In this illustration, [start:end:step] was used to obtain a result. We designate the starting Python substring index with start, and the endpoint with end.

For instance, using string[2:15] alone would return 'eaxkalmlprloe', but setting step two instructs Python to skip through the characters two at a time. A breakdown of this procedure can be seen in the picture below:

A string can be divided into what is referred to as a substring. You can use the code snippet to apply to example_string to return a substring by looking at the image below, which shows the string example_string with indices.

Conclusion

It's time to put an end to this discussion of Python substring. Today, we learned a lot about Python substrings, from syntax to naive methods for obtaining the substring. Finally, we examined numerous instances of both using a substring and reversing a string using a substring. It's time for you to put what you've learned into practice.

FAQs

1. What does Python's substring function do?

In Python, a substring is a group of characters with another string attached. 'Slicing of String' is another name for it. Our strings can be processed using the 'slicing' feature of arrays in Python. Slicing is a versatile functionality that can be applied to any array type object.

2. What Python command is most effective for finding substrings?

To determine whether the substring is actually present in the string, use the in keyword. The Boolean value that the in keyword returns is either True or False. When the substring is found in the string, the in operator returns True. Before using the find() method, using the in keyword is a helpful first step.

3. How does Python determine whether a substring exists?

Using an if-else statement, you can determine whether a Python substring is present in a string in Python. You can conditionally execute various blocks of code using the if-else statement depending on whether the condition is true or false.

4. How frequently does a substring occur in a string?

The count() method can count how many times a substring appears in a longer string. The count() function in Python iterates through a string. The amount of times a substring appears in the string is returned as a value.

5. How can a substring be extracted from a string?

Use the Substring(Int32, Int32) method to extract substring from string Python regex that starts at a specific character position and ends before the string's end. The value of the currently active instance is not changed by this method. Instead, it gives back a brand-new string that starts where startIndex was in the original string.