1 while expression:
   2     suite...
   3 [else:
   4     suite...]

   1 n = 0
   2 while n < 10:
   3     print( n )
   4     n += 1

   1 for n in range(10):
   2     print( n )

   1 n = 0
   2 while n < 10:
   3     print( n )
   4     n += 1
   5 else:
   6     print( "無事，終了しました" )