negative-number

Stumbled upon something slightly perplexing today while writing some unittests: blah = ['a', 'b', 'c'] blah[:-3] # [] blah[:-2] # ['a'] blah[:-1] # ['a', 'b'] blah[:-0] # [] Can't for the life of me figure out why blah[:-0] # [] should be the case, the pattern definitely seems to suggest that it should be ['a', 'b', 'c'] . Can anybody help to shed some light on why that is the case? Haven't been able to find mention in the docs as to why that is the case. -0 is 0 , and a slice that goes from the beginning of a list inclusive to index 0 non-inclusive is an empty list . Python doesn't treat -0

I was able to add a try catch that tells the user that they cant use letters.However for some reason adding a try catch for negative numbers dosent seem to work.I know that the try block is where if somthing can go wrong like entering in a negative number the catch can print out the error message. I think thats where my problem lies. Another problem that is associated with the try catch is that I'm use to the user entering in -1 to enter the contents that the user inputs so I'm thinking its gonna cause a logical problem. tl;dr Adding a try catch or another catch to prevent user from adding

Consider the following expression: (a - b) mod N Which of the following is equivalent to the above expression? 1) ((a mod N) + (-b mod N)) mod N 2) ((a mod N) - (b mod N)) mod N Also, how is (-b mod N) calculated, i.e., how is the mod of a negative number calculated? Thanks. I don't want to bother you with some complex mathematical concepts, so i'll try to keep it simple. When we say that a = b (mod c), we simply say that a-b is a multiple of c. This means that when we want to know what is the value of a mod c, saying that it is a or a-c or a+c or a+1000*c is true. Thus, your 2 formulas are

This question already has an answer here: Modulo operation with negative numbers 12 answers A modulo operation a%b returns the remainder for a/b but for negative numbers it does not do so. #include <stdio.h> int main(void) { int n=-4; printf("%d\n",n%3); return 0; } It should return 2 as 3*(-2)=-6 is just smaller than -4 and a multiple of 3 but the output is -1. Why is it treating (-a) mod b same as -(a mod b) As a general rule, the modulo and division should satisfy the equation b * (a/b) + a%b == a For positive numbers, it is obvious that this means that a%b must be a positive number. But if