arcgis中用python代码实现条件赋值

在字段计算器的代码块对话框写入下列代码：
rec=""

def autoIncrement(a):

global rec

if (a > 68 and a <=75.65): 

  rec ="4级"

elif(a > 75.65 and a <=80.00): 

  rec ="3级"

elif(a > 80.00 and a <=84.35):

  rec ="2级"

elif(a > 84.35 and a <=91.50):

  rec ="1级"

else:

  rec = ""

return rec

在代码块下面的对话框中写入：
autoIncrement(！a！)