http://docs.python.org/2/reference/lexical_analysis.html#explicit-joining

反斜杠:

  if 1900<year<2100 and 1<=month<=12  

     and 1<=day<=31 and 0<=hour<24
      and 0<=minute<60 and 0<=second<60:   # Looks like a valid date
       return1

  反斜杠不能用于#comment的续行

在圆括号、方括号以及大括号中分行，可以不用反斜杠，直接回车分行

month_names=['Januari','Februari','Maart',      # These are the

'April',   'Mei',      'Juni',       # Dutch names

 'Juli',    'Augustus','September',  # for the months
 'Oktober','November','December']   # of the year