python - "IndexError: list index out of range" For planetary simulator -

traceback (most recent call last):   file "n:\starry\planetary orbits ver 8.py", line 121     updatedisplay(pos) # updates 3d displays position of masses   file "n:\starry\planetary orbits ver 8.py", line 100, in updatedisplay     stars[i].pos = pos[i] indexerror: list index out of range 

i've been getting error , can't find out why, i've checked see numpy arrays , lists have values in them, shown below in python shell:

number of stars: 2 please enter x position of star: 0 please enter y position of star: 0 please enter z position of star: 0 please enter radius of star: 10 please enter mass of star: 5000000 please enter x speed of star: 0 please enter y speed of star: 0 please enter z speed of star: 0 please enter x position of star: 100 please enter y position of star: 0 please enter z position of star: 0 please enter radius of star: 10 please enter mass of star: 5000000 please enter x speed of star: 0 please enter y speed of star: 0 please enter z speed of star: 0 [(0, 0, 0), (100, 0, 0)]  # printed positionlist # [(0, 0, 0), (0, 0, 0)]    # printed momentumlist # [5000000, 5000000]        # printed masslist # [10, 10]                  # printed radiuslist # [[  0   0   0]            # printed pos array#  [100   0   0]]   [[0 0 0]                  # printed momentum array #  [0 0 0]] [[5000000]                # printed masses array #  [5000000]] [10 10]                   # printed radii array # 

these values show items going lists , arrays, surely code select item inside array?

for in range(nstars):     updatedisplay(pos)  

here full program reference:

nstars = int(input("number of stars: "))  # change have more or fewer stars   g = 6.7e-11 # universal gravitational constant  # typical values msun = 2e30 rsun = 2e9 vsun = 0.8*sqrt(g*msun/rsun) dt = 10.0   #reprensents change in time nsteps = 0 time = clock() nhits = 0  #~~~~~~~~~~~~~~~~~~~~~~~~~~~ global data ~~~~~~~~~~~~~~~~~~~~~~~~~~~#  stars = [] colors = [color.red, color.green, color.blue,           color.yellow, color.cyan, color.magenta] positionlist = [] momentumlist = [] masslist = [] radiuslist = [] pos = none radii = none masses = none f = none momentum = none  #~~~~~~~~~~~~~~~~~~~~~~~~~~~ global data ~~~~~~~~~~~~~~~~~~~~~~~~~~~#  def calculations(speedx, speedy, speedz, x, y, z, mass, radius):     px = mass*(speedx)     py = mass*(speedy)     pz = mass*(speedz)     positionlist.append((x,y,z))     momentumlist.append((px,py,pz))     masslist.append(mass)     radiuslist.append(radius)  def starcreation(stars,x,y,z,radius):     stars = stars+[sphere(pos=(x,y,z), radius=radius, color=colors[i % 6],                    make_trail=true, interval=10)]   def datacollection():     x = input("please enter x position of star: ")     y = input("please enter y position of star: ")     z = input("please enter z position of star: ")     radius = input("please enter radius of star: ")     starcreation(stars,x,y,z,radius)     mass = input("please enter mass of star: ")     speedx = input("please enter x speed of star: ")     speedy = input("please enter y speed of star: ")     speedz = input("please enter z speed of star: ")     calculations(speedx, speedy, speedz, x, y, z, mass, radius)  def momenta(momentum, masses):     vcm = sum(momentum)/sum(masses) # velocity of center of mass     momentum = momentum-masses*vcm # make total initial momentum equal 0  def listtoarray(positionlist, momentumlist, masslist, radiuslist):     global pos     pos = array(positionlist)     global momentum     momentum = array(momentumlist)     global masses     masses = array(masslist)     masses.shape = (nstars,1) # numeric python: (1 nstars) vs. (nstars 1)     global radii     radii = array(radiuslist)     momenta(momentum, masses)  def forces(pos, radii, masses):     # compute forces on stars     r = pos-pos[:,newaxis] # pairs of star-to-star vectors (where r relative position vector     n in range(nstars):         r[n,n] = 1e6  # otherwise self-forces infinite     rmag = sqrt(sum(square(r),-1)) # star-to-star scalar distances     hit = less_equal(rmag,radii+radii[:,newaxis])-identity(nstars)     hitlist = sort(nonzero(hit.flat)[0]).tolist() # 1,2 encoded 1*nstars+2     global f     f = g*masses*masses[:,newaxis]*r/rmag[:,:,newaxis]**3 # force pairs  def selfforces(f):     f[n,n] = 0  def updatemomentapositions(momentum, pos, masses):     momentum = momentum+sum(f,1)*dt              pos = pos+(momentum/masses)*dt  def updatedisplay(pos):     stars[i].pos = pos[i]   #~~~~~~~~~~~~~~~~~~~~~~~~~ actual proagram ~~~~~~~~~~~~~~~~~~~~~~~~~#  in range(nstars):     datacollection()  listtoarray(positionlist, momentumlist, masslist, radiuslist) print (positionlist) print (momentumlist) print (masslist) print (radiuslist) print (pos) print (momentum) print (masses) print (radii)  while true:      rate(100) # no more 100 loops per second on fast computers     forces(pos, radii, masses)# computes forces between masses      n in range(nstars):         selfforces(f) # no self forces      updatemomentapositions(momentum, pos, masses) # updates momentum , positions of stars      in range(nstars):         updatedisplay(pos) # updates 3d displays position of masses 

your issue never add stars stars when call starcreation function. reassign local stars list shadows global stars line :

stars = stars+[sphere(pos=(x,y,z), radius=radius, color=colors[i % 6],                make_trail=true, interval=10)] 

you have 2 solutions issue :

1. you can modify global stars list inplace via either stars+=[sphere(...)] or stars.append(sphere(...))
2. or tell python stars global variable , shouldn't shadowed, :

.

def starcreation(stars,x,y,z,radius):     global stars     stars = stars+[sphere(pos=(x,y,z), radius=radius, color=colors[i % 6],                make_trail=true, interval=10)] 

edit : mistake assumed didn't exist , sorry.