def issym(b3):
  """test if a list has equal number of positive
     and negative values; zeros belong to both. """
  npos = 0; nneg = 0
  for item in b3:
    if (item >= 0): 
      npos +=1
    if (item <= 0):
      nneg +=1
  if (npos==nneg):
    return True
  else:
    return False