python - difference between find and index

Question

I am new to python and cannot quite understand the difference between find and index.

>>> line
'hi, this is ABC oh my god!!'
>>> line.find("o")
16
>>> line.index("o")
16

They always return the same result. Thanks!!

Answer 1

str.find returns -1 when it does not find the substring.

>>> line = 'hi, this is ABC oh my god!!'
>>> line.find('?')
-1

While str.index raises ValueError:

>>> line.index('?')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: substring not found

Both the functions behave the same way if a sub-string is found.