str.find() Function in Python

The str.find() function in Python is used to search for a specified substring within a string and return the index (position) of its first occurrence. If the substring is not found, it returns -1. This function is useful for checking the presence of a substring in a string and determining its position.

Syntax:

string.find(substring, start, end)

• substring: The substring you want to search for.
• start (optional): The starting index from where the search should begin. The default is 0.
• end (optional): The ending index where the search should stop. The default is the end of the string.

Example 1: Basic usage

# Example 1: Finding a substring
my_string = "Hello, world!"
index = my_string.find("world")
print(index)  # Output: 7

In this example:

• The substring "world" is found at index 7 in the string "Hello, world!".

Example 2: Substring not found

# Example 2: Substring not found
my_string = "Hello, world!"
index = my_string.find("Python")
print(index)  # Output: -1

Here:

• The substring "Python" is not found in the original string, so the result is -1.

Example 3: Specifying start and end indices

# Example 3: Specifying start and end indices
my_string = "Hello, world! Welcome to the world of Python."
index = my_string.find("world", 10)
print(index)  # Output: 27

In this case:

• The search for "world" starts from index 10, and the first occurrence of "world" after that is found at index 27.

Example 4: Using find() with overlapping substrings

# Example 4: Overlapping substrings
my_string = "banana"
index = my_string.find("ana")
print(index)  # Output: 1

Here:

• The substring "ana" is found starting at index 1.

Key Points:

• str.find() returns the index of the first occurrence of the specified substring.
• It is case-sensitive, meaning "Hello" and "hello" are considered different.
• If the substring is not found, it returns -1.
• You can specify optional start and end parameters to limit the search range within the string.
• The function does not modify the original string.

Example 5: Case sensitivity

# Example 5: Case sensitivity
my_string = "Hello, world!"
index = my_string.find("hello")
print(index)  # Output: -1

In this example:

• The search for "hello" (lowercase) returns -1 because it is not found in the original string.

Example 6: Multiple occurrences

# Example 6: Multiple occurrences
my_string = "apple banana apple orange"
index = my_string.find("apple")
print(index)  # Output: 0

Here:

• The first occurrence of "apple" is found at index 0, even though there is a second occurrence later in the string.