Python 3 reference · String Methods

Python String index() Method

Return the lowest index of a substring, like find(), but raise ValueError when it is not found.

Syntax

str.index(sub, start=0, end=len(s))

Parameter	Description
`sub`	The substring to look for.
`start, end` optional	Only search this slice.

The index (an int).

Found and not foundTry it yourself

print("hello".index("l"))
try:
    "hello".index("z")
except ValueError as e:
    print("ValueError:", e)

Output

2
ValueError: substring not found

Use it when the substring must existTry it yourself

line = "key=value"
sep = line.index("=")
print(line[:sep], "->", line[sep + 1:])

Output

key -> value

Version	Change
Python 3.0	Added

str.find() · Return the lowest index where a substring is found, or -1 if it isn't. Optional start and end limit the search.
str.rindex() · Return the highest index of a substring, like rfind(), but raise ValueError when it is not found.
str.count() · Return the number of non-overlapping occurrences of a substring, optionally only between start and end positions.
Python Strings · tutorial