While finding solutions to all string related problems, checking for the presence of a string inside another string is necessarily required.
One of the most common use cases is checking for invalid or not required characters in user input.
This post will explain a whole set of 5 different ways in which you can test if a string exists in another string in python.

Method 1: Using in operator
Place in operator between the substring and the main string to check if one string contains another string. in will return True if the string to test is present in the main string else it will be False. Example,

str = 'www.codippa.com'
str_to_check = 'codippa'
# check if string exists
if str_to_check in str:
    print(str_to_check,'is present in',str)
else:
    print(str_to_check,'is NOT present in',str)

Output will be

codippa is present in www.codippa.com

To remember the order of substring and string around in operator, remember that you are checking substring in a string.

Method 2: Using find
find method is present in string class and should be invoked on a string object. It accepts a single string argument and checks if the string supplied as argument is present in the string object on which this method is called.
find returns the index of beginning of argument string if it is present otherwise it returns -1. Example,

str = 'www.codippa.com'
str_to_check = 'codippa'
# check the index of substring in main string
index = str.find(str_to_check)
if index != -1:
    print(str_to_check,'is present in',str,'starting at position',index)
else:
    print(str_to_check,'is not present in',str) 

Output of above code is

codippa is present in www.codippa.com starting at position 4

Remember that the index is counted from 0.

Method 3: Using contains
contains method is present in string class. It is also invoked on a string object and accepts a single string argument.
It checks for the presence of string argument in the string object on which this method is invoked and returns True if the substring is present else returns False. Example,

str = 'www.codippa.com'
str_to_check = 'codippa'
if str.__contains__(str_to_check):
    print(str_to_check, 'is present in', str)
else:
    print(str_to_check, 'is not present in', str)

Output for the above code will be

codippa is present in www.codippa.com

Method 4: Using index method
index is again a method of string class which is invoked on a string object.
This method accepts a string argument and checks if the argument string is present inside the string on which it is invoked.
If the string is present, then it returns the index of substring(start index will be 0) else it throws a ValueError.
Thus, for using this method, you need to apply some python exception handling concepts. Example,

str = 'www.codippa.com'
str_to_check = 'codippa'
# handle valueerror
try:
    index = str.index(str_to_check)
    print(str_to_check,'is present in',str,'starting at position',index)
except ValueError:
    print(str_to_check, 'is not present in', str)

Method 5: Using operator module
operator module has a contains function which accepts two arguments. First is the string in which you want to find the substring and second is the substring itself.
contains will return True if the substring is present, otherwise it will return False. For using this method, you need to import operator module. Example,

import operator

str = 'www.codippa.com'
str_to_check = 'codippa'
if operator.contains(str, str_to_check):
    print(str_to_check, 'is present in', str)
else:
    print(str_to_check, 'is not present in', str)
contains method from operator module internally uses in operator.

Hope the methods explained in this post will help you in testing if a string contains another string in python. Do not forget to hit the clap.

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