A substring is a sequence of characters within a String. When writing a Python program you may need to check whether a substring is present inside another string or not, there can be many reasons for that like searching and filtering data, input validation, etc.
To check if a string contains a substring, we can utilise many built-in functions that Python provides us, each one with slightly different functionality.
At the end of this tutorial, you will not only know how to check for substrings but also know a lot of new Python methods, so let’s get started.
Methods to check if a Python string contains a substring
Python has various methods for this check, but we’ll be using those that are easy to implement and require only a few lines of code.
The following are the methods in Python to check if a string contains other substrings.
- Using find() method
- Using in operator
- Using count() method
- Using index() method
- Using operator.contains() method
Now, let’s examine each of them separately, along with their respective syntax and examples.
Using the find() Method
The find() method is used to check whether a string contains a particular substring or not. It takes a substring as an argument and if the string contains that particular substring, it returns the starting index of the substring else it returns -1.
Syntax:
string.find(substring)
Here, substring is the string you want to search, and string is the string object in which you want to search.
Example:
str="Safa Mulani is a student of Engineering discipline."
sub1="Safa"
sub2="Engineering"
print(str.find(substring1))
print(str.find(substring2))
Output:
0
28
Using the ‘in’ operator
The ‘in’ operator checks for the presence of a substring within a string by returning either True or False. If the substring is present it returns True else it returns False.
Syntax:
substring in string
Example:
str="Safa Mulani is a student of Engineering discipline."
sub1="Safa"
sub2="Done"
print(sub1 in str)
print(sub2 in str)
Output:
True
False
Using the count() Method
The count() method checks for the occurrence of a substring in a string. If the substring is not found in the string, it returns 0.
Syntax:
string.count(substring)
Example:
str="Safa Mulani is a student of Engineering discipline."
sub1="Safa"
sub2="student"
sub3="Done"
print(str.count(sub1))
print(str.count(sub2))
print(str.count(sub3))
Output:
1
1
0
Using the index() Method
This method can also check for a substring’s presence in a string. If the substring is not present in the string then it doesn’t return any value, rather it generates a ValueError.
Syntax:
string.index(substring)
Example:
str = "Safa is a Student."
try :
result = str.index("Safa")
print ("Safa is present in the string.")
except :
print ("Safa is not present in the string.")
Output:
Safa is present in the string.
Using the operator.contains() Method
We can also use the operator.contains() method of the “operator” module to check for substrings. It takes a string and a substring as an argument and returns a boolean True if the substring is contained in that string, else it returns False.
Syntax:
operator.contains(string, substring)
Example:
import operator
str = "Safa is a Student."
if operator.contains(str, "Student"):
print ("Student is present in the string.")
else :
print ("Student is not present in the string.")
Output:
Student is present in the string.
Conclusion
In this tutorial, we explored five ways to check if a string contains a substring. Each method offers its own advantages and suitability for different scenarios. Among them, the best way to check whether a Python string contains another string is to use for loop, as it is easily understandable by beginners, more readable and does not require any additional methods.
With this knowledge, you can efficiently check if string contains a substring in Python programming language. Additionally, there is another method, string.__contains__(), which provides a more efficient way of performing this check. For a detailed tutorial specifically covering this method, you can read “Python String Contains: Check if a String Contains a Substring“. Hope you have enjoyed reading the content.
Reference
https://stackoverflow.com/questions/3437059/does-python-have-a-string-contains-substring-method