The `index` Method in Python: Finding the Index of a Substring in a String

Returns the smallest index where the specified substring is found in the original string.

sub -- substring whose starting index must be determined
start=0 -- starting index of the slice in the original string where the substring must be found
end=None -- ending index of the slice in the original string where the substring must be found

This method works like str.find(), but raises an exception if the substring is not found.

my_str = 'barbarian'
my_str.index('bar')  # 0
my_str.index('bar', 1)  # 3
my_str.index('bar', 1, 2)  # ValueError

The optional parameters start and end can take any values supported by slicing, including negative values.

Use this method only when you need the starting index of a substring. To check if a substring is present, use the in operator:

my_str = 'barbarian'
if 'bar' in my_str: ...  # True

The index Method in Python: Finding the Index of a Substring in a String