在for循环外打印一个值

Question

I am studying for a final in a beginners programming class. I received this question wrong on my midterm. I said the answer is 1, however, the answer is actually 0. I was wondering if anyone could explain to me why it is 0. Is it because z is originally assigned to 0? I am not sure how to tell if it's a local variable with this limited code. Thank you for any help you provide!

z=0
for x in range(1, 200, -1):
    z=z+1
print(z)

Answer 1

There is no elements at range(1, 200, -1) , the loop not even starts. So z never changed its value.

Read about the step(third arg of range) arg here:

https://docs.python.org/2/library/functions.html#range

A nice way to see this is convert the range to list:

print(list(range(1, 200, -1)))
>>> []

Answer 2

You should test it out in your interpreter. The loop never makes an iteration. Think of what is being incremented.

Your range is 1 through 200, but you are choosing to increment by -1 at each step starting at 1, so you cannot move backwards in this case.

Answer 3

它保持为零，因为范围是1、200，但您步进-1，因此for循环内的表达式从未真正执行。