Python String find()

Summary: in this tutorial, you’ll learn how to use the Python string find() method effectively to find a substring in a string.

Introduction to Python string find() method

The find() is a string method that finds a substring in a string and returns the index of the substring.

The following illustrates the syntax of the find() method:

str.find(sub[, start[, end]])Code language: CSS (css)

The find() method accepts three parameters:

• sub is the substring to look for in the str.
• start and end parameters are interpreted as in the slice str[start:end], which specifies where to search for the substring sub.

Both start and end parameters are optional. The start parameter defaults to zero. And the end parameter defaults to the length-1 where length is the length of the str.

If the str doesn’t contain the substring sub within the slice str[start:end], the find() method returns -1.

In practice, you should use the find() method only if you want to know the position of the substring. If you just want to check whether a string contains a substring, you should use the in operator instead:

sub in str

Python string find() method examples

Let’s take some examples of using the find() method.

1) Using the Python string find() method to find a substring in a string

The following example shows how to use the find() method to find the substring 'Johny' in the string 'Johny Johny Yes Papa':

s = 'Johny Johny Yes Papa'
result = s.find('Johny')

print(result)Code language: PHP (php)

Output:

0

Because the string 'Johny Johny Yes Papa' has two substrings 'Johny', the find() method returns the index of the first occurrence of the substring 'Johny'.

2) Using the Python string find() method to find a substring in a string within a slice

The following example uses the find() method to locate the substring 'Johny' in the string 'Johny Johny Yes Papa' within the slice str[1:]:

s = 'Johny Johny Yes Papa'
result = s.find('Johny', 1)

print(result)Code language: PHP (php)

Output:

6

In this example, the find() method returns the index of the second occurrence of the substring 'Johny' in the string 'Johny Johny Yes Papa'.

3) The substring doesn’t exist in the string example

The following example returns -1 because the substring 'Julia' doesn’t exist in the string 'Johny Johny Yes Papa':

s = 'Johny Johny Yes Papa'
result = s.find('Julia')

print(result)Code language: PHP (php)

Output:

-1

Summary

• Use Python string find() to find a substring in a string.
• The find() method returns -1 if the substring is not found.