Find Function in Python

During the software development process, there are certain actions that require the need to locate specific words or sentences. For example, if you were developing a text editor, one of the most critical functionalities would be the ability to find and replace text. This task involves searching for particular words or sentences within the document, and in such situations, the find() function can prove to be extremely helpful.

What is the Find Function in Python?

In Python, the find function is a string method that is used to locate a particular sub-string within a given string. Its purpose is to return the position of the first occurrence of the sub-string in the string. If the sub-string is not found, the find method returns -1. The

Syntax of the Find Function

string.find(substring, start, end)

Here, the string is the string that you want to search in, the substring is the string that you want to search for, the start is the starting index of the search, and the end is the ending index of the search.

If the start and end are not specified, the find function will search the entire string. If the start is specified, the search will start from that index. If the end is specified, the search will end at that index.

Parameters of Find Function in Python

The find function in python takes three parameters:

• substring: This is the required parameter, and it is the substring that you want to search for in the string. It could be a string or a single character.
• start: This is an optional parameter, and it is the starting index of the search. The starting index of the search indicates where the search for the substring within the string should begin. Its usage is not mandatory, and if not specified, the search will begin at index 0 by default.
• end: This is also an optional parameter, and it is the ending index of the search. It specifies where to end the search for the substring in the string. The default value of this parameter is the length of the string.

Return Value of Find Function in Python

If the substring is present in the string, the find function returns the index of the first character of the substring and if the substring is not present in the string, it returns -1.

Here is an example that demonstrates the return value of the find() function:

string = "Hello, PrepBytes!"
substring = "PrepBytes"
index = string.find(substring)
print(index)

Output:

7

Explanation – This example demonstrates the usage of the find() function to look for the sub-string "PrepBytes" in the string "Hello, PrepBytes!". The find function returns the index 7 since the sub-string is located at that index within the string. If the sub-string is changed to "World", which is not present in the string, the find() function will return -1 to indicate that the sub-string was not found.

Examples of Find Function in Python

Let’s look at some examples of how to use the find function in Python:

Example – 1
Below is code implementation and explanation:

string = "Hello, PrepBytes!"
substring = "prepBytes"
index = string.find(substring)
print(index)

Output:

-1

Explanation: This particular example involves searching for the index of the sub-string "prepBytes" in the string "Hello, PrepBytes!". Unfortunately, the sub-string is not present in the string, resulting in the find function returning -1 to signify that the sub-string could not be found.

Example – 2
Below is code implementation and explanation:

string = "Hello, PrepBytes!"
substring = "y"
index = string.find(substring, 5, 13)
print(index)

Output:

12

Explanation: This example focuses on searching for the sub-string "y" in the string "Hello, PrepBytes!" but exclusively between the indices 5 and 13. The find function is used to locate the first occurrence of the sub-string within that specific range, which happens to be at index 12. Therefore, the find function returns the value 12 as the index of the first occurrence of the sub-string within the specified range.

Example – 3
Below is code implementation and explanation:

string = "Hello, prepBytes!"
substring = "e"
index = string.find(substring, 2)
print(index)

Output:

9

Explanation: In this example, we are searching for the substring "e" in the string "Hello, PrepBytes!" starting from index 2. The find function returns the index of the first occurrence of the substring after that index, which is 9.

Example – 4
Below is code implementation and explanation:

string = "Hello, C! Hello, C++! Hello, Python! Hello, Java!"
substring = "Hello"
start = 0
while True:
    index = string.find(substring, start)
    if index == -1:
        break
    print(index)
    start = index + 1

Output:

0
10
22
37

Explanation: In this example, we are searching for the substring "Hello" within the string "Hello, C! Hello, C++! Hello, Python! Hello, Java!" and print the index of each occurrence. We are using a while loop to keep searching for the substring until it is no longer found. The start variable is used.

Summary
Here is a summary of the key points about the find function in Python:

• The find function in python is a built-in string method that is used to search for a specified substring within a string.
• The find function in python provides the position of the first instance of the sub-string in the string. If the sub-string cannot be found within the string, the function will return -1.
• The find() function takes three parameters: the substring to search for, the starting index of the search (optional), and the ending index of the search (optional).
• If the starting and ending indices are not specified, the function searches the entire string.
• The function is case-sensitive, but you can convert both the string and substring to lowercase or uppercase using the lower() or upper() methods before calling the find() function for a case-insensitive search.

FAQs

Here are some Frequently Asked Questions on find function in python.

Q1: What is the difference between find() and index() in python?
A: The find() and index() functions in python are similar in that they both search for a substring within a string. There are, however, some significant differences between the two functions. The find() function returns -1 if the substring is not found, whereas the index() function raises a ValueError exception. Additionally, the find() function is a built-in method of the string class, whereas the index() function is a built-in method of the list class.

Q2: Is the find() function case-sensitive?
A: Yes, the find() function is case-sensitive. If you want to perform a case-insensitive search, you can convert both the string and the substring to lowercase or uppercase using the lower() or upper() methods before calling the find() function.

Q3: Can I use the find() function to search for a regular expression pattern in a string?
A: No, the find() function cannot be used to search for a regular expression pattern in a string. If you need to search for a regular expression pattern, you can use the re-module in Python.

Q4: What is the time complexity of the Python find() function?
A: The time complexity of the find() function in Python is O(n), where n is the length of the string. This is because the function needs to search the entire string for the specified substring. However, the function may terminate early if the substring is found before the end of the string is reached.