- 1Python String capitalize() – Capitalize First Letter of a String
- 2Python String casefold() – Case-Insensitive String Comparison
- 3Python String center() Method – Center Align a String with Padding
- 4Python String count() Method – Count Substring Occurrences
- 5Python string.encode() – Convert String to Bytes
- 6Python String endswith() – Check if a String Ends with Substring
- 7Python String expandtabs() – Replace Tabs with Spaces
- 8Python String find() – How to Locate Substrings Easily
- 9Python String index() Method – Find Position of a Substring
- 10Python String isalnum() Method – Check Alphanumeric Strings
- 11Python String isalpha() Method – Check for Alphabetic Characters
- 12Python String isascii() Method – Check for ASCII Characters
- 13Python String isdecimal() Method – Check if All Characters Are Decimals
- 14Python String isdigit() Method – Check If a String Has Only Digits
- 15Python String isidentifier() – Check for Valid Identifiers
- 16Python String islower() Method – Check for Lowercase Strings
- 17Python String isnumeric() Method – Check for Numeric Characters
- 18Python String isprintable() Method – Check Printable Characters
- 19Python String isspace() Method – Check for Whitespace Only
- 20Python String istitle() Method – Check for Title Case
- 21Python String isupper() Method – Check for Uppercase Letters
- 22Python String join() Method – Combine Strings Easily
- 23Python String ljust() Method – Left Justify a String with Spaces or Characters
- 24Python String lower() Method – Convert to Lowercase
- 25Python String lstrip() Method – Remove Leading Characters
- 26Python String maketrans() Method – Create Translation Tables
- 27Python String partition() Method – Split into Three Parts
- 28Python String replace() Method – Replace Substrings Easily
- 29Python String rfind() Method – Find Last Occurrence of Substring
- 30Python String rindex() Method – Find Last Occurrence of a Substring
- 31Python String rjust() Method – Right Justify a String
- 32Python String rpartition() Method – Split String from the Right
- 33Python String rsplit() Method – Split from the Right
- 34Python String rstrip() Method – Remove Trailing Characters
- 35Python String split() Method – Split Strings Easily
- 36Python String splitlines() Method – Split String by Line Breaks
- 37Python String startswith() Method – Check If a String Starts With
- 38Python String strip() Method – Remove Spaces from Ends
- 39Python String swapcase() Method – Convert Uppercase to Lowercase and Vice Versa
- 40Python String title() Method – Convert to Title Case
- 41Python String translate() Method – Replace Characters Using Mapping
- 42Python String upper() Method – Convert to Uppercase
- 43Python String zfill() Method – Pad String with Zeros
Python String index() Method – Find Position of a Substring
Next Topic ⮕Python String isalnum() Method – Check Alphanumeric Strings
Python String index()
Method
The index() method in Python is used to find the position of the first occurrence of a substring inside a string. If the substring is not found, it raises a ValueError
.
Syntax
string.index(substring, start, end)
Parameters:
substring
– The string to search for.start
– (Optional) The position to start searching from. Default is 0.end
– (Optional) The position to stop searching. Default is end of the string.
Returns:
- The index (integer) of the first match of the substring.
Example 1: Basic Usage
text = "Python is fun"
print(text.index("fun"))
10
Explanation: The word "fun" starts at index 10 in the string.
Example 2: With Start and End Parameters
text = "banana"
print(text.index("a", 2))
3
Explanation: It starts searching from index 2, so it finds the second "a" at position 3.
Difference Between index()
and find()
index()
raises aValueError
if the substring is not found.find()
returns-1
instead of raising an error.
Common Error
text = "hello"
print(text.index("z")) # Raises ValueError
ValueError: substring not found
Use Case: Validate Substring Presence
text = "apple pie"
if "pie" in text:
print("Found at index:", text.index("pie"))
Found at index: 6
Summary
string.index()
returns the index of the first occurrence of a substring.- It raises a
ValueError
if not found. - Use optional
start
andend
to limit the search range.
Practice Problem
Write a program to find the position of the word "world" in the string "hello world" using index()
.
text = "hello world"
print("Index of 'world':", text.index("world"))
Expected Output:
6
Next Steps
Try using index()
with different substrings and edge cases like empty strings or overlapping matches.