Python - 虚假循环

Question

fn='a'
x=1

while fn:
    print(x)
    x+=1
    if x==100:
        fn=''

Output: 1 ... 99

fn=''
x=1

while fn:
    print(x)
    x+=1
    if x==100:
        fn='a'

Output: while loop does not run.

---

What is the reason for the while loop not running?

Is it that the condition that ends a while loop is 'False' and therefore it's not capable of performing 'while false' iterations?

Answer 1

If you want 'while false' functionality, you need not . Try while not fn: instead.

Answer 2

The condition is the loop is actually a "pre-" condition (as opposed to post-condition "do-while" loop in, say, C). It tests the condition for each iteration including the first one.

On first iteration the condition is false, thus the loop is ended immediately.

Answer 3

In python conditional statements :

'' is same as False is same as 0 is same as []

Answer 4

Consider your loop condition to be translated into this:

fn=''
x=1

while len(fn)>0:
    print(x)
    x+=1
    if x==100:
        fn='a'

while checks if the string is not empty at the beginning of each iteration.