On Mon, Nov 24, 2014 at 12:32:27PM -0600, boB Stepp wrote: > Python 2.7.8 > Win7Pro > > >>> str = "0123456789" > >>> str[-1] > '9' > >>> str[-3:-1] > '78' > >>> str[-3:] > '789' > > I understand that the above is "the way it is" in Python, but I am > puzzled why the designers did not choose that str[-3:-1] returns > '789', especially since str[-1] returns '9'. What is the reason for > choosing Python's actual behavior?
The slice indexes fall *between* characters, not on them. So the string "abcdef" will have indexes: |a|b|c|d|e|f| 0 1 2 3 4 5 6 (Things may not line up perfectly unless you read this will a monospaced font like Courier.) Think of slicing as cutting on the lines, so the slice [1:4] cuts just before "b" and just after "d". Negative indexes work the same way, just in the opposite direction: |a|b|c|d|e|f| -6-5-4-3-2-1 ? Note that the final line, marked with a question mark, would have been 0 except that 0 is already used for positive slicing. So the slice [-3:-1] cuts before the "d" and just after "e". -- Steven _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
