Difference Between find() and index() in Python
Last Updated :
21 Nov, 2024
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Both methods are used to locate the position of a substring within a string but the major difference between find() and index() methods in Python is how they handle cases when the substring is not found. The find() method returns -1 in such cases, while index() method raises a ValueError.
Example of find()
s = "hello world"
# Finds the position of the substring "world"
print(s.find("world"))
# Returns -1 when substring is not found
print(s.find("python"))
# Finds the position of "o" starting from index 5
print(s.find("o", 5))
s = "hello world"# Finds the position of the substring "world"print(s.find("world"))# Returns -1 when substring is not foundprint(s.find("python"))# Finds the position of "o" starting from index 5print(s.find("o", 5))Output
6 -1 7
Explanation:
- s.find("world") returns 6 because the substring "world" starts at index 6.
- s.find("python") returns -1 as substring "python" is not present in string.
- s.find("o", 5) starts the search from index 5 and finds the first occurrence of "o" at index 7.
Example of index()
s = "hello world"
# Finds position of the substring "world"
print(s.index("world"))
# Raises a ValueError when substring is not found
print(s.index("python"))
# Finds position of "o" starting from index 5
print(s.index("o", 5))
s = "hello world"# Finds position of the substring "world"print(s.index("world"))# Raises a ValueError when substring is not foundprint(s.index("python"))# Finds position of "o" starting from index 5print(s.index("o", 5))6
ERROR!
Traceback (most recent call last):
File "<main.py>", line 7, in <module>
ValueError: substring not foundExplanation:
- s.index("world") returns 6 because substring "world" starts at index 6.
- When s.index("python") is executed then it raises a ValueError as the substring "python" is not in string.
- s.index("o", 5) starts searching from index 5 and finds the first occurrence of "o" at index 7.
When to use find() and index()?
- Use find() when we need to check if a substring exists and do not want to handle exceptions.
- Use index() when we are sure that the substring exists or we want an exception to be raised if it doesn't exist.
