嵌套循环中仅打印一次

Question

I am modeling a particle moving through different layers, and once it moves through the layer I want it to print a few things. My problem is the particle can move back into the previous layer and come out again, which triggers it to print again, I do not want this.

while math.sqrt((pho.pos.x)*(pho.pos.x)+(pho.pos.y)*(pho.pos.y)+(pho.pos.z)*(pho.pos.z))<10:
    x=random.uniform(-j,j)
    y=random.uniform(-j,j)
    z=random.uniform(-j,j)
    step=(x,y,z)
    t=t+dt
    pho.pos=pho.pos+step
    print 'Step Number', t
    rate(speed)
    d=math.sqrt((pho.pos.x)*(pho.pos.x)+(pho.pos.y)*(pho.pos.y)+(pho.pos.z)*(pho.pos.z))
    '''if d>10:
        print pho.pos 
        print d 
        print 'Out of Layer 1 in',t,'steps!'
        break
    else:
        pass'''
d=math.sqrt((pho.pos.x)*(pho.pos.x)+(pho.pos.y)*(pho.pos.y)+(pho.pos.z)*(pho.pos.z))
print pho.pos
print d
print 'Out of Layer 1 in',t,'steps!'

The part I don't want repeating is the last three print statements, I have tried break statements but this code is a nested loop, and when it gets re-looped it starts over before the break.

Answer 1

On whatever class pho is, make a property called printed or something and initialize it to False . Then, set it to True when printing for the first time, and say

if d > 10 and not pho.printed

instead of just if d > 10 .

Answer 2

Try something like this. Your code I think was all supposed to be part of the while loop. If not, move the out_of_layer to before the next outer loop.

out_of_layer = False  

while math.sqrt((pho.pos.x)*(pho.pos.x)+(pho.pos.y)*(pho.pos.y)+(pho.pos.z)*(pho.pos.z))<10:
    x=random.uniform(-j,j)

    ... blah blah stuff you already know about ...

    d=math.sqrt((pho.pos.x)*(pho.pos.x)+(pho.pos.y)*(pho.pos.y)+(pho.pos.z)*(pho.pos.z))
    if not out_of_layer:
        print pho.pos
        print d
        print 'Out of Layer 1 in',t,'steps!'
        out_of_layer = True