Question

I am on PS4
I dont understand why

if (i + shift) < len(uppercase):
coder[uppercase[i]] = uppercase[i + shift]

returns key value pair in dict when i is 0 and shift is - 2 (as happens in prob set sol with decoder)

as there is no index -2 in uppercase string

interestingly ' ' as key gives 'x'

why is this so

Answer 1

the shell (or idle) is a great place to play and experiment
http://dpaste.com/787903/

from the Tutorial in the Python documentation: an intro to slices in this strings section
http://docs.python.org/tutorial/introduction.html#strings

and see note 3 from:
http://docs.python.org/library/stdtypes.html#sequence-types-str-unicode-list-tuple-bytearray-buffer-xrange

The Python documentation should be installed on your computer - the Tutorial is a must-read.

http://stackoverflow.com/questions/509211/good-primer-for-python-slice-notation

http://effbot.org/zone/python-list.htm

Answer 2

Thanks bwCA
Sorted