Python String index() Method

Q: What is the difference between index() and find() in Python?

`index()` raises `ValueError` when the substring is missing, while `find()` returns `-1`. Both return the same position when the text is found, so choose by how you want a miss handled.

Q: How do I find all positions of a substring in Python?

Call `index()` in a loop with a growing `start` argument, or loop with `enumerate` and compare. A single `index()` call only gives the first match.

By Yogesh Sharma (LinkedIn) · Every code example is run and checked on Python 3.13 (how we test) · Last updated 21 Oct 2026

Short answer

str.index(sub) returns the position of the first occurrence of sub in a string, and raises ValueError if sub is not found.

Use index() when you are sure the text you are looking for is there and a missing value would be a bug. It works exactly like find(), except for what happens on a miss: find() quietly returns -1, while index() stops with an error. Positions start at 0, as with every Python string.

Quick facts
Syntax	`text.index(sub, start, end)`
Parameters	`sub`: the substring to look for; `start` and `end` (optional): search only inside `text[start:end]`
Returns	The lowest index where `sub` begins (an `int`)
If not found	Raises `ValueError: substring not found`
Case sensitive	Yes: `"Python".index("p")` fails

How str.index() searches a string

Python scans from left to right and returns the index of the first character of the first match. The match may be one character or many.

Python

word = "banana"
print(word.index("b"))
print(word.index("na"))
print(word.index("a"))

The last call returns 1, not 3 or 5, because only the first match counts. Because a string is a sequence, the number you get can be used directly in slicing, as shown in the examples below.

Using the start and end arguments

The optional start and end arguments limit the search to text[start:end]. The returned index is still counted from the beginning of the whole string, not from start. This is the usual way to find the second occurrence: search once, then search again from just after the first hit.

Python

path = "a/b/c"
first = path.index("/")
second = path.index("/", first + 1)
print(first, second)

index() vs find() vs rindex()

Pick the method by what you want to happen when the text is missing.

Method	Searches from	If not found	Best for
`index()`	Left (first match)	Raises `ValueError`	Text that must be present
`find()`	Left (first match)	Returns `-1`	Text that may be missing
`rindex()`	Right (last match)	Raises `ValueError`	Last occurrence that must exist
`rfind()`	Right (last match)	Returns `-1`	Last occurrence that may be missing
`in` operator	Anywhere	`False`	Only a yes/no answer, no position

Handling ValueError when the substring is missing

If the text comes from a user or a file, a miss is normal, not a bug. Either test with in first (see checking if a string contains a substring), use find(), or wrap the call in try/except ValueError. Catching the error keeps the happy path short and avoids searching the string twice. The ValueError lesson explains this error in general.

Examples you can run

Press Run, then edit the code and run it again.

Find the first position of a substring

index() gives the starting position of the first match, and rindex() the starting position of the last one.

Find the first position of a substring

text = "banana"
print(text.index("an"))
print(text.index("an", 2))
print(text.rindex("an"))

Expected output1
3
3

Split an email address at the @ sign

Because the email must contain @, index() is a natural fit. The slices on either side of the position give the user name and the domain.

Split an email address at the @ sign

email = "asha@example.com"
at = email.index("@")
print(email[:at])
print(email[at + 1:])

Expected outputasha
example.com

Catch the error for a missing substring

A missing substring raises ValueError; the message is substring not found.

Catch the error for a missing substring

filename = "report.txt"
try:
    pos = filename.index("-")
    print("Dash at", pos)
except ValueError as err:
    print("Error:", err)

Expected outputError: substring not found

Common mistakes

Searching with the wrong letter case

✗ Wrong

title = "Python Basics"
print(title.index("basics"))

ValueError: substring not found

✓ Right

title = "Python Basics"
print(title.lower().index("basics"))

index() is case sensitive. Lower-case both sides, or search with the exact case.

Expecting -1 for a missing substring

✗ Wrong

city = "Pune"
if city.index("x") == -1:
    print("not found")

ValueError: substring not found

✓ Right

city = "Pune"
if city.find("x") == -1:
    print("not found")

The -1 convention belongs to find(). Use find() for a quiet miss, or catch ValueError.

Reading the result as relative to start

✗ Wrong

s = "ab-cd-ef"
i = s.index("-", 3)
print(s[3 + i:])

Wrong slice: the index is already counted from the start of the string, so adding `3` again skips characters.

✓ Right

s = "ab-cd-ef"
i = s.index("-", 3)
print(s[i:])

The returned index is absolute. Use it as is.

Python String index() Method: questions people ask

What is the difference between index() and find() in Python?

index() raises ValueError when the substring is missing, while find() returns -1. Both return the same position when the text is found, so choose by how you want a miss handled.

Does str.index() return the first or the last occurrence?

It returns the first occurrence, counting from the left. Use rindex() to get the last occurrence instead.

How do I find all positions of a substring in Python?

Call index() in a loop with a growing start argument, or loop with enumerate and compare. A single index() call only gives the first match.

Keep learning

Step-by-step lessons:
Python Strings Python String Methods

More in string methods:
Python String split() Method Python String join() Method Python String strip() Method Python String lstrip() Method Python String rstrip() Method Python String replace() Method Python String upper() Method Python String lower() Method See all →