python string index

The .index() function in Python is utilized to determine the position (index) of a specific substring within a given string. If the specified substring isn’t present in the string, the function will raise an exception.
This function is case-sensitive. So, when you’re looking to determine where a certain substring begins within a string, .index() is the function to use.

Syntax

To use the .index() function, there are two primary syntax formats:

str.index(substring)

Or, for more granularity, you can also specify where to start and end the search:

str.index(substring, start, end)

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Parameters

Here’s a breakdown of the parameters you can use with the .index() function:

• substring: This is the text piece you’re searching for within the main string.
• start (optional): Specify from which index to start the search.
• end (optional): Specify at which index to end the search.

Example Usage

Let’s delve into some practical examples to illustrate the use of the .index() function.

str = "Tip of the day: "
print( str.index("Tip") )

The output for the above code will be:

0

Another Example:

str = "Tip of the day: "
print( str.index("Tip",5) ) # this will raise an exception

The resulting output for this example is:

Traceback (most recent call last):
  File "tmp.py", line 2, in 
    print( str.index("Tip") )
ValueError: substring not found

Ready to move on? Discover how to measure the length of a string in Python here.