wap26 wap26 - 1 year ago 67
Python Question

Why are slice and range upper-bound exclusive?

Disclaimer: I am not asking if the upper-bound

argument of
is exclusive or how to use these functions.

Calls to the
functions, as well as the slice notation
all refer to sets of integers.

range([start], stop[, step])
slice([start], stop[, step])

In all these, the
integer is excluded.

I am wondering why the language is designed this way.

Is it to make
equal to the number of elements in the represented integer set when
equals 0 or is omitted?

Is it to have:

for i in range(start, stop):

look like the following C code?

for (i = start ; i < stop; i++) {

Answer Source

The documentation implies this has a few useful properties:

word[:2]    # The first two characters
word[2:]    # Everything except the first two characters

Here’s a useful invariant of slice operations: s[:i] + s[i:] equals s.

For non-negative indices, the length of a slice is the difference of the indices, if both are within bounds. For example, the length of word[1:3] is 2.

I think we can assume that the range functions act the same for consistency.

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