1 0 0
0 0 1
0 0 1

1 0 0
0 0 1
0 0 1 0

def addTo(array,textFile):
  file=open(textFile,'ab')
  (numRows,numColumns)=array.shape
  main=array[0:numRows-1,:]
  endRow=array[numRows-1,:]
  newEndRow=np.append(endRow, [0])
  np.savetxt(file,main, fmt='%10.5f', newline=os.linesep)
  np.savetxt(file,newEndRow, fmt='%10.5f', newline=os.linesep)
  file.close()

addTo(np.eye(3),'test1.txt')

1.00000    0.00000    0.00000
   0.00000    1.00000    0.00000
   0.00000
   0.00000
   1.00000
   0.00000