Python find() method: detect whether a string contains a substring

In this tutorial, we'll learn about the find() method in Python, which is a string method that searches for a specified substring within a string and returns the index of the first occurrence. If the substring is not found, the method returns -1.

The find() method takes the following arguments:

sub (required): The substring to search for within the string.
start (optional): The starting index from which to search for the substring. By default, it is 0.
end (optional): The ending index up to which to search for the substring. By default, it is the length of the string.

Example 1: Basic usage of the find() method

text = "Hello, world! Welcome to the world of Python."
substring = "world"

index = text.find(substring)
print(index)  # Output: 7

Example 2: Using start and end arguments

text = "Hello, world! Welcome to the world of Python."
substring = "world"

index = text.find(substring, 10)  # Start searching from index 10
print(index)  # Output: 28

text = "Hello, world! Welcome to the world of Python."
substring = "world"

index = text.find(substring, 0, 10)  # Search between index 0 and 10
print(index)  # Output: 7

Example 3: Substring not found

text = "Hello, world! Welcome to the world of Python."
substring = "Java"

index = text.find(substring)
print(index)  # Output: -1

Note that the find() method is case-sensitive. If you want to perform a case-insensitive search, you can convert both the text and the substring to lowercase (or uppercase) before using the find() method.

text = "Hello, world! Welcome to the World of Python."
substring = "WORLD"

index = text.lower().find(substring.lower())
print(index)  # Output: 28

In summary, the find() method is used to search for a specified substring within a string and returns the index of the first occurrence. If the substring is not found, it returns -1. You can also specify a start and end index to search within a specific range.

How to Use find() to Detect Substring in Python:
- The find() method returns the index of the first occurrence of a substring in a string. If not found, it returns -1.
```
# Example
sentence = "Python is powerful"
index = sentence.find("is")
```

Checking for Substring Presence with find() in Python:

Use find() to check if a substring is present in a string.

# Example
sentence = "Python programming"
if sentence.find("java") != -1:
    print("Substring found")
else:
    print("Substring not found")

Find Substring Index in a String with Python find():
- Retrieve the index of the first occurrence of a substring using find().
```
# Example
sentence = "Python is versatile"
index_python = sentence.find("Python")
```

Using find() to Search for a Substring Occurrence in Python:

Search for a specific substring occurrence using find().

# Example
sentence = "Python programming is fun. Python is powerful."
index_second_python = sentence.find("Python", sentence.find("Python") + 1)

Handling Missing Substrings with find() in Python:

Check for the presence of a substring and handle missing substrings.

# Example
sentence = "Python is amazing"
substring = "Java"
index = sentence.find(substring)
if index != -1:
    print(f"Substring found at index {index}")
else:
    print(f"Substring '{substring}' not found")

Case-Insensitive Substring Search with find() in Python:

Perform a case-insensitive substring search using lower().

# Example
sentence = "Python is CASE-INSENSITIVE"
substring = "case-insensitive"
index = sentence.lower().find(substring.lower())

Python find() vs index() for Substring Detection:

While find() returns -1 for missing substrings, index() raises a ValueError.

# Example with find()
sentence = "Python is great"
index_find = sentence.find("Java")  # Returns -1 if not found

# Example with index()
try:
    index_index = sentence.index("Java")  # Raises ValueError if not found
except ValueError:
    index_index = -1

Detecting Multiple Substring Occurrences with find() in Python:

Iterate to find multiple occurrences of a substring using find().

# Example
sentence = "Python is easy. Python is versatile. Python is powerful."
substring = "Python"
start_index = 0
while True:
    index = sentence.find(substring, start_index)
    if index == -1:
        break
    print(f"Found at index: {index}")
    start_index = index + len(substring)