Lets solve this general problem of finding if a particular piece of string is present in a larger string in different ways. This is a very common kind of problem every programmer comes across aleast once in his/her lifetime. This article gives various techniques to solve it.
Method 1 : Using in
operator
The in
operator is the most generic, fastest method to check for a substring, the power of in
operator in python is very well known and is used in many operations across the entire language.
# Python 3 code to demonstrate # checking substring in string # using in operator # initializing string test_str = "GeeksforGeeks" # using in to test # for substring print ( "Does for exists in GeeksforGeeks ? : " ) if "for" in test_str : print ( "Yes, String found" ) else : print ( "No, String not found" ) |
Output :
Does for exists in GeeksforGeeks ? : Yes, String found
Method 2 : Using str.find()
str.find() method is generally used to get the lowest index at which the string occurs, but also returns -1, if string is not present, hence if any value returns >= 0, string is present, else not present.
# Python 3 code to demonstrate # checking substring in string # using str.find() # initializing string test_str = "GeeksforGeeks" # using str.find() to test # for substring res = test_str.find( "for" ) if res > = 0 : print ( "for is present in GeeksforGeeks" ) else : print ( "for is not present in GeeksforGeeks" ) |
Output :
for is present in GeeksforGeeks
Method 3 : Using str.index()
This method can be used to performs the similar task, but like str.find(), it doesn’t return a value, but a ValueError if string is not present, hence catching the exception is the way to check for string in substring.
# Python 3 code to demonstrate # checking substring in string # using str.index() # initializing string test_str = "GeeksforGeeks" # using str.index() to test # for substring try : res = test_str.index( "forg" ) print ( "forg exists in GeeksforGeeks" ) except : print ( "forg does not exists in GeeksforGeeks" ) |
Output :
forg does not exists in GeeksforGeeks
Method 4 : Using operator.contains()
This is lesser known method to check for substring in a string, this method is also effective in accomplishing this task of checking a string in a string.
# Python 3 code to demonstrate # checking substring in string # using operator.contains() import operator # initializing string test_str = "GeeksforGeeks" # using operator.contains() to test # for substring if operator.contains(test_str, "for" ): print ( "for is present in GeeksforGeeks" ) else : print ( "for is not present in GeeksforGeeks" ) |
Output :
for is present in GeeksforGeeks
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