Python String find() Method with Examples

Details

What is Python String find()?

Python String find() is a function available in Python library to find the index of the first occurrence of a substring from the given string. The string find() function will return -1 instead of throwing an exception, if the specified substring is not present in the given string.

In this Python string find() method tutorial, you will learn:

Syntax of Python string find()

The basic syntax of Python find() function is as follows:

string.find(substring,start,end)

Parameters for the find() method

Here, are three parameters of the function String find() in Python:

Example of find() method with default values

The parameters passed to Python find() method are substring i.e the string you want to search for, start, and end. The start value is 0 by default, and the end value is the length of the string.

In this example, we will use the method find() in Python with default values.

The find() method will search for the substring and give the position of the very first occurrence of the substring. Now, if the substring is present multiple times in the given string, still it will return you the index or position of the first one.

Example: 

mystring = "Meet gtupapers Tutorials Site.Best site for Python Tutorials!"
print("The position of Tutorials is at:", mystring.find("Tutorials"))

Output: 

The position of Tutorials is at: 12

Example of find() using start argument

You can search the substring in the given string and specify the start position, from where the search will begin. The start parameter can be used for the same.

The example will specify the start position as 15, and the find() in Python method will begin the search from position 15. Here, the end position will be the length of the string and will search till the end of the string from 15 positions onwards.

Example: 

mystring = "Meet gtupapers Tutorials Site.Best site for Python Tutorials!"
print("The position of Tutorials is at:", mystring.find("Tutorials", 20))

Output: 

The position of Tutorials is at 48

Example of find() using start and end arguments

Using the start and end parameter, we will try to limit the search, instead of searching the entire string.

Example: 

mystring = "Meet gtupapers Tutorials Site.Best site for Python Tutorials!"
print("The position of Tutorials is at:", mystring.find("Tutorials", 5, 30))

Output: 

The position of Tutorials is at 12

Example of find() method To find the position of a given substring in a string

We know that find() helps us to find the index of the first occurrence of substring. It returns -1 if the substring is not present in the given string. The example below shows the index when the string is present and -1 when we don't find the substring we are searching for.

Example: 

mystring = "Meet gtupapers Tutorials Site.Best site for Python Tutorials!"
print("The position of Best site is at:", mystring.find("Best site", 5, 40))
print("The position of gtupapers is at:", mystring.find("gtupapers", 20))

Output: 

The position of Best site is at: 27
The position of gtupapers is at: -1

Python string rfind()

The Python function rfind() is similar to find() function with the only difference is that rfind() gives the highest index for the substring given and find() gives the lowest i.e the very first index. Both rfind() and find() will return -1 if the substring is not present.

In the example below, we have a string "Meet gtupapers Tutorials Site. Best site for Python Tutorials!" and will try to find the position of substring Tutorials using find() and rfind(). The occurrence of Tutorials in the string is twice.

Here is an example where both find() and rfind() are used. 

mystring = "Meet gtupapers Tutorials Site.Best site for Python Tutorials!"
print("The position of Tutorials using find() : ", mystring.find("Tutorials"))
print("The position of Tutorials using rfind() : ", mystring.rfind("Tutorials"))

Output: 

The position of Tutorials using find() :  12
The position of Tutorials using rfind() :  48

The output shows that find() gives the index of the very first Tutorials substring that it gets, and rfind() gives the last index of substring Tutorials.

Python string index()

The Python string index() is function that will give you the position of the substring given just like find(). The only difference between the two is, index() will throw an exception if the substring is not present in the string and find() will return -1.

Here is a working example that shows the behaviour of index() and find(). 

mystring = "Meet gtupapers Tutorials Site.Best site for Python Tutorials!"
print("The position of Tutorials using find() : ", mystring.find("Tutorials"))
print("The position of Tutorials using index() : ", mystring.index("Tutorials"))

Output:

The position of Tutorials using find() :  12
The position of Tutorials using index() :  12

We are getting same position for both find() and index(). Let us see an example when the substring given is not present in the string. 

mystring = "Meet gtupapers Tutorials Site.Best site for Python Tutorials!"
print("The position of Tutorials using find() : ", mystring.find("test"))
print("The position of Tutorials using index() : ", mystring.index("test"))

Output: 

The position of Tutorials using find() :  -1
Traceback (most recent call last):
  File "task1.py", line 3, in <module>
    print("The position of Tutorials using index() : ", mystring.index("test"))
ValueError: substring not found

In the above example, we are trying to find the position of substring "test". The substring is not present in the given string, and hence using find(), we get the position as -1, but for index(), it throws an error as shown above.

To find the total occurrence of a substring

To find the total number of times the substring has occurred in the given string we will make use of find() function in Python. Will loop through the string using for-loop from 0 till the end of the string. Will make use of startIndex parameter for find().

Variables startIndex and count will be initialized to 0. Inside for –loop will check if the substring is present inside the string given using find() and startIndex as 0.

The value returned from find() if not -1, will update the startIndex to the index where the string is found and also increment the count value.

Here is the working example: 

my_string = "test string test, test string testing, test string test string"
startIndex = 0
count = 0
for i in range(len(my_string)):
    k = my_string.find('test', startIndex)
    if(k != -1):
        startIndex = k+1
        count += 1
        k = 0

print("The total count of substring test is: ", count )

Output: 

The total count of substring test is:  6

Summary

 

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