Python String Methods Compared: find() vs index()

A parser must look for a delimiter that might not exist.

What You Need to Understand

Both find() and index() search for a substring and return its first matching position. The key difference occurs when the substring is missing: find() returns -1, while index() raises ValueError. Both support optional start and end limits.

When to Use It

A parser must look for a delimiter that might not exist.

Step-by-Step Python Example

message = "order:ready"
print(message.find(":"))
print(message.find("#"))
try:
    print(message.index("#"))
except ValueError:
    print("Delimiter not found")

How the Example Works

The colon is at position five; the missing hash gives -1 from find(). The index() call is caught instead of ending the program.

Example Output

5
-1
Delimiter not found
True

A Second Example

Compare this smaller variation with the main example, then experiment with your own values.

value = "@username"
position = value.find("@")
print(position != -1)

Important Behavior and Edge Cases

Never treat find() result as a boolean; position zero is valid but falsy, while -1 is truthy.

Try It Yourself

Search for a colon at the beginning of a new sample and compare both methods.

Common Beginner Mistakes

Never treat find() result as a boolean; position zero is valid but falsy, while -1 is truthy.
Applying a string method before defining whether text is intended for display, comparison, parsing, or input validation.

Key Takeaways

Both find() and index() search for a substring and return its first matching position.
The colon is at position five; the missing hash gives -1 from find().
Never treat find() result as a boolean; position zero is valid but falsy, while -1 is truthy.