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If I wanted a list from 0 to 100 in steps of five I could use range(0,105,5), but I could also use range(0,101,5).
Honestly, neither of these makes sense to me because excluding the last number seems non-intuitive.
That aside, what is the "correct" way to create a list from 0 to 100 in steps of five? And if anyone has the time, in what instance would excluding the last number make code easier to read?
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Python range is inclusive because it starts with the first argument of the range() method, but it does not end with the second argument of the range() method; it ends with the end – 1 index. The reason is zero-based indexing.
By default, The range(n) is exclusive, so it doesn't include the last number in the result. It creates the sequence of numbers from start to stop -1 . For example, range(5) will produce [0, 1, 2, 3, 4] .
If you want to exclude 0 then change your range to (1,11). The way range works is the lower limit is inclusive where as upper limit is exclusive. On an unrelated note, if your lower limit is 0, you need not include the lower limit and write it as range(11) which is same as range(0,11).
You'll also want to have a try-except block around the int() call, in case you get a ValueError (if they type a for example). Note if you use Python 2. x, you'll want to use raw_input() instead of input() . The latter will attempt to interpret the input as Python code - that can potentially be very bad.
The two choices you have listed are not similar. One is range(start, stop+step, step) and the other is range(start, stop+1, step). They don't necessary return the same thing. The only case they do is when stop - start is divisible by step.
>>> start, stop, step = 0, 42, 5
>>> range(start, stop+step, step)
[0, 5, 10, 15, 20, 25, 30, 35, 40, 45]
>>> range(start, stop+1, step)
[0, 5, 10, 15, 20, 25, 30, 35, 40]
So, which one should you use? If you want [start, stop] (inclusive), then use stop+1 for the end of the range. Anything more than stop+1 will have side effects like the above. range(0, 42+5, 5) includes 45 as a result, which is not in the [0, 42] range. How do you feel about that?
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The correct way to create a list from 0 to 100 in steps of five is
range(0, 100, 5)
this list has 100 / 5 == 20 elements and does not include the number 100.
Dijkstra explained why counting should start at zero and intervals should be half-open a (very?) long time ago: https://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/EWD831.html
Since Python's range follows Dijkstra and uses half-open intervals, it follows that to create one past the half open interval you must add one:
range(0, 100+1, 5) # closed interval [0..100] by five
and, yes, I would expect to see it written exactly like that in production code since it is unusual.
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