[Python] String Indexing Methods : Comparing str.find() and str.index()

Working with strings is fundamental in Python, and locating the index of specific characters or substrates is often required. This article will explore the use of two key methods for this purpose: str.find() and str.index(). We'll examine how these methods work and identify the differences between them.

Using the str.find() Method

The str.find() method returns the index of the start of the first occurrence of the specified value. If the value is not found, it returns -1.

text = "Python is wonderful"
index = text.find("is")
print(index) # Output: 7

Here, the str.find() method returns 7, the index where the substring "is" begins.

Using the str.index() Method

The str.index() method is similar to str.find(), but it raises an exception if the value is not found.

text = "Python is wonderful"
index = text.index("is")
print(index) # Output: 7

# Raises ValueError
try:
    index = text.index("Java")
except ValueError:
    print("Value not found")

Differences Between str.find() and str.index()

The key difference is how they handle the case when the value is not found:

• str.find(): Returns -1
• str.index(): Raises an exception

Example: Search Within a Specific Range with str.find() and str.index()

Both methods allow you to specify the start and end positions to search within a specific range.

text = "Python is wonderful, Python is great"

# Using find
find_index = text.find("Python", 25, 30)
print(find_index) # Output: -1

# Using index with exception handling
try:
    index_index = text.index("Python", 25, 30)
except ValueError:
    index_index = -1

print(index_index) # Output: -1

This example demonstrates how to limit the search to a specific range using both methods and handle exceptions with str.index().

Understanding how to find the position of characters or substrates in a string is straightforward with Python's str.find() and str.index() methods. They enable efficient searching within a string, with distinct behaviors depending on whether the value is found.

FAQs

1. What's the main difference between str.find() and str.index()? The main difference is how they handle a value not found; str.find() returns -1, str.index() raises an exception.
2. Can I search within a specific range in the string? Yes, both methods allow this.
3. Is there a performance difference between the two methods? Generally, there is no significant difference for standard use cases.
4. Can these methods be used with variables containing strings? Yes, you can apply these methods to any variable holding a string.
5. What happens if I try to search for a value not in the string? str.find() will return -1, while str.index() will raise a ValueError exception.