Python index ValueError: substring not found   

Often programmers with different background are confused by error:

ValueError: substring not found

when they are trying to find character in a string like:

mystring = 'This is a simple string test].'
begin = mystring.index('[')

The behavior is not expected by many programmers to have an error for this search. A more expected behavior is to get -1 or not found instead of error. This can be done by using method find():

mystring = 'This is a simple string test].'
begin = mystring.find('[')
print(begin)

result:

-1

Behavior of the functions is the same if a substring is found.

Another difference of the two functions is that index is available for lists, tuples while found is only for strings.