Python Substring

A string in computer programming means a sequence or an order of Unicode characters. It is made up of a character sequence. In other words, we can say that it is a series of extraordinary characters and alphanumeric characters. Let us see what a substring is in python and what its uses are. Let us also focus on how a substring is created in python, if already created then how to find a substring and how to extract a substring from a string using the slicing method in python.

Substring in python

A definite part in a string is defined as a substring, also known as the “Slicing of String”. There are a lot of methods in python to create a substring as well as to find if a substring is there in a string or not, to find an index of a substring, etc. The main use of substring is to get a sliced-out string from the actual string with the help of arguments passed in the indices. Slicing a string into a substring is actually a vast range of functionality which are used mostly in the array-type object. This article will focus on several operations that could be performed on substrings.

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Creation of a Substring in python

There are a lot of ways of creating a substring in python. The most common method of this is using slicing. Another method is by using the python split() function. This function is used based on a particular delimiter inside the string.

Let us see the syntax below for creating a substring using slicing.  There are four approaches that can be followed for slicing which are

  • Slicing using begin-index, end-index
String= string[begin: end: step]
  • Slicing using begin index without end index
String= string[begin:]

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  • Slicing using end index without begin-index
String= string[:end]
  • Slicing the entire string
String= string[:]

In the syntax above, begin will be the index from where the substring will start. In this, the substring incorporates the element. If the starting index / begin is not specified in the python code while slicing, the compiler assumes it to be 0. The gein-index is always known to be inclusive however the end index is always known to be exclusive in python. 

Step is a form of character which has to be included right after the present character. The step has a default value as one and the compiler always assumes it to be 1 if the programmer has not mentioned it already.

End will be the index where the substring will end. In this, the substring excludes the element. If the end is not specified in the python code while slicing, the compiler assumes it to be the string length.

Let us see an example below to understand how a substring is created in python for first 9 characters:

string = "Welcome to HKR Training"

print(string[0:9])

Output:

Welcome t

>

Let us see another example below to get a 4-character long substring with the index as 3rd character.

string = "Welcome to HKR Training"

print(string[2:6])

Output:

lcom

>

Let us see an example below to get the last character of the string as a substring:

string = "Welcome to HKR Training"

print(string[-1])

Output:

g

>

Below is a python code to get the reverse of a string using slicing:

string = "Welcome to HKR Training"

print(string[::-1])

Output:

gniniarT RKH ot emocleW

>

How to check if a Substring is found?

To check if a substring is found, the programmer makes use of the find() function. This is an in-built function in python. Let us see a python code below to see how find() function world to search for a substring in a given string:

string1= ' Welcome to HKR training '


if 'python' in string1:


    print('Substring is found')


if string1.find('all') != -1:


    print('Substring is found')


else:


     print('Substring is not found')

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Output:

Substring is not found

>

The user makes use of an in-built count() function to count the number of characters time substring occurred in the given string. 

string1= ' Welcome to HKR training '

print('Substring count =', string1.count('o'))

Output:

Substring count = 2

There is another in-built replace() function to replace the string with another string in python

string1 = "Welcome to HKR training"

string1.replace("training", "Tutorial")

print (string1)

Output:

Welcome to HKR Tutorial

>

Output:

Actual string: Welcome to HKR training

How to get the substring from the given string in python:

As we have discussed earlier also, we can get the substring from the given string using slicing. Let us now understand it more with the help of a python code:

string = 'Welcome to HKR training'

print ("Actual string: ", string) 


begin = string[:2] 

end = string[3:] 


#result 


print ("The resultant substring from the start is:", begin) 


print ("The resultant substring from the end is:", end)

Output:

Actual string:  Welcome to HKR training

The resultant substring from the start is: We

The resultant substring from the end is: come to HKR training

>

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Below is another python code to take substring to the beginning or to the end of the string:

init_string = 'Welcome to HKR training'

print ("initial_strings : ", init_string)


string1_strt = init_string[:4]

string1_end = init_string[5:]


print ("The resultant substring from the start is", string1_strt)

print ("The resultant substring from the end is", string1_end)

Output:

initial_strings :  Welcome to HKR training

The resultant substring from the start is Welc

The resultant substring from the end is me to HKR training

>

Now let us see a python code to create a substring by taking characters from a certain defined space.

init_string = 'Welcome to HKR training

print ("initial_strings : ", init_string)


string1_alt = init_string[::4]

string1_gap2 = init_string[::5]

print ("The resultant substring from the start is", string1_alt)

print ("The resultant substring from the end is", string1_gap2)

Output:

initial_strings :  Welcome to HKR training

The resultant substring from the start is WotKrg

The resultant substring from the end is Wm tg

Now let us see a python code to create a substring from the middle with some step gap between characters:

string = 'Welcome to HKR training'

print ("Actual string: ", string) 


string1 = string[1:9:1]

print ("The final substring is:", string1)

Output:

Actual string:  Welcome to HKR training

The final substring is: elcome t

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Conclusion

In this article, we have discussed 'substring in python'. With the help of this article, you will be able to understand what is a substring along with the python code to create a substring in python using slicing and its 4 methods along with how to implement them all. The other method that we have discussed is creating a substring using split() function. We have also discussed 2 in-built functions which are: find(), replace() and count(). We have also demonstrated in detail how to find a substring in a given python string along with the method to get the substring from the given string in python. A lot of python code examples are illustrated for your better and more practical understanding along with their outputs. Happy coding and keep learning!

Related Articles:

1. Python Partial Functions

2. Python Split Method

3. Python Frameworks

4. Python Generators

5. Python List Length

6. Python Operators

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Gayathri
Gayathri
Research Analyst
As a senior Technical Content Writer for HKR Trainings, Gayathri has a good comprehension of the present technical innovations, which incorporates perspectives like Business Intelligence and Analytics. She conveys advanced technical ideas precisely and vividly, as conceivable to the target group, guaranteeing that the content is available to clients. She writes qualitative content in the field of Data Warehousing & ETL, Big Data Analytics, and ERP Tools. Connect me on LinkedIn.

Python Substring FAQ'S

To extract a substring in Python, there is an option strn[0:n] which extracts a substring from a string.

To find the substring there is a method, The find() is a string method that finds substring present in a string.

There are many methods to extract words from a string
If we know the perfect position then we can perform a slicing operation on that string to get the desired word.

Using regex(
findall() ) also we can find words from string if there are any special characters in string