getting a number pattern with python

I am working on animation effect that i need this pattern of numbers for one variable: 0, 0 , 1 , - 1 , 2 - 2 , 3 , -3… …-100,100.
well its not working


x = 0
a = 0
b = 0
while x < 100:
    x = x + 1
    a = a - 1
    if x > a:
        b = x
        print b
    elif x < a:
        b = a
        print b
    else:

eventually i want to get reverse of it too

why not doing it like this?

 
  x = 0
  a = 0
  b = 0
  list = []
  while x < 101:
   a = x
   b = x*(-1)
   list.append(a)
   list.append(b)

   print a, ', ', b
   x +=1

thanks semmelb. Yours is closer i modified it to this


# -*- coding: utf-8 -*-
x = 0
a = 0
b = 0
list = []
while x < 101:
    a = x
    b = x*(-1)
    list.append(a)
    list.append(b)

    p = a
    print p
    p = b
    print p
    x +=1

now the p needs to go two times to loc x while running the script while ones
this descripes the motion:


frame 1                                                        x
frame 2                                                             x
frame 3                                                      x 
frame 4                                                                 x
frame 5                                                   x                              
frame 6                                                                     x
frame 7                                                 x
...

so motion with strobe effect