   Python Comparing instances?
  I hope this makes senseI have an Array of instances representing particles,and i want to compare the distance between each particle pair for example say i have an array[a, b, c] representing 3 particles a, b, chow do i compare/ code it so that i get the difference between pairsa,ba,cb,conlyrather that comparing the distances multiple times (getting repetive comparisons)between particlesie a,aa,ba,cb,ab,bb,cc,ac,bc,c   
  itertools.combinations   ;for i in range(len(myObjectArray)):    obj1 = myObjectArray    for j in range(i+1,len(myObjectArray)):   obj2 = myObjectArray[j]   calculateDistance( obj1, obj2 );  thanks guys that was very quick ill try those methods and see how i go