What are the default slice indices in Python *really*?

Question

From the python documentation docs.python.org/tutorial/introduction.html#strings:

Slice indices have useful defaults; an omitted first index defaults

Answer 1

The end value is always exclusive, thus the 0 end value means include index 1 but not 0. Use None instead (since negative numbers have a different meaning):

>>> s[len(s)-1:None:-1]
'gnirtsym'

Note the start value as well; the last character index is at len(s) - 1; you may as well spell that as -1 (as negative numbers are interpreted relative to the length):

>>> s[-1:None:-1]
'gnirtsym'