[Error] Why does substring slicing with index out of range work?

Question : Why doesn't example[999:9999] result in error? Since example[999] does, what is the motivation behind it?

 

Answer : 

• [999:9999] isn't an index, it's a slice, and has different semantics. From the python intro : "Degenerate slice indices are handled gracefully : an index that is too large is replaced by the string size, an upper bound smaller than the lower bound returns an empty string"
• The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j. If i or j is greater than len(s), use len(s).

 

Source :

• https://docs.python.org/2/library/stdtypes.html#sequence-types-str-unicode-list-tuple-bytearray-buffer-xrange  
• https://stackoverflow.com/questions/9490058/why-does-substring-slicing-with-index-out-of-range-work