Python String index() Usage and Example

Python string methods

The index() method returns the index value of the substring within the string (if found). If the substring is not found, an exception will be raised.

StringThe syntax of the index() method is:

str.index(sub[, start[, end]])

index() parameters

The index() method takes three parameters:

• sub　 -The substring to be searched for in the string str.

• startandend(Optional)-Instr [start：end]中str [start:end]中

Search for substring

• index() return value

• If the substring exists in the string, it will return the smallest index of the substring found in the string.If the substring does not exist in the string, it will raiseValueError

exception.index() method is similar toIn Python, indexing starts from 0, not

string's find() method-1The only difference is that, if the substring is not found, the find() method returns

：index() with start and end parameters1, while index() raises an exception.

Example
：index() with only substring parameter
result = sentence.index('is fun')
print("Substring 'is fun':", result)
result = sentence.index('Java')

When running the program, the output is:

print("Substring 'Java':", result)　19
Traceback (most recent call last):
　　File "...", line　6Substring 'is fun':
ValueError: substring not found

, inresult = sentence.index('Java') Note:1In Python, indexing starts from 0, not

：index() with start and end parameters2.

Example
sentence = 'Python programming is fun.'
# Search for substring 'gramming is fun.'　10))
# Search for substring 'gramming is '
# Search for substring 'g is'　10,　-4))
# Search for substring 'programming'
print(sentence.index('fun',　7,　18))

When running the program, the output is:

15
17
Traceback (most recent call last):
　　File "...", line　10, inprint(quote.index('fun',　7,　18))
ValueError: substring not found

Python string methods