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分类: LINUX

2009-08-29 12:37:34

本文讨论在没有方便的IDE工具可用的情况下,使用pdb调试python程序
 
源码例子
例如,有模拟税收计算的程序:
 
#!/usr/bin/python

def debug_demo(val):

                if val <= 1600 :
                                print "level 1"
                                print 0
                elif val <= 3500 :
                                print "level 2"
                                print (val - 1600) * 0.05
                elif val <= 6500 :
                                print "level 3"
                                print (val - 3500) * 0.10 + (3500-1600) * 0.05
                else:
                                print "level 4"
                                print (val - 6500) * 0.20 + (6500-3500) * 0.10 + (3500-1600) * 0.05
                                

#~def debug_demo                
                
if __name__ == "__main__":
                
                debug_demo(4500)
 
debug_demo函数计算4500的入账所需的税收。
 
如何调试?
 
1.加入断点
 
在需要插入断点的地方,加入红色部分代码:如果_DEBUG值为True,则在该处开始调试(加入_DEBUG的原因是为了方便打开/关闭调试)。
 
#!/usr/bin/python
_DEBUG=True
def debug_demo(val):
                if _DEBUG == True:
                                import pdb
                                pdb.set_trace()

                if val <= 1600 :
                                print "level 1"
                                print 0
                elif val <= 3500 :
                                print "level 2"
                                print (val - 1600) * 0.05
                elif val <= 6500 :
                                print "level 3"
                                print (val - 3500) * 0.10 + (3500-1600) * 0.05
                else:
                                print "level 4"
                                print (val - 6500) * 0.20 + (6500-3500) * 0.10 + (3500-1600) * 0.05


#~def debug_demo                

if __name__ == "__main__":

                debug_demo(4500)
 
 
2.开始运行调试
 
  运行程序./debug_demo.py,得到
 
> /usr/local/qspace/user_network/debug_demo.py(7)debug_demo()
-> if val <= 1600 :
(Pdb)
-> val <= 1600 : 指示当前执行的语句,(Pdb)等待你的调试指令. pdb的指令很丰富,输入h指令可以查看指令的使用方法。下面简单介绍常用指令:
  
  查看代码上下文,l(小写L)
 
(Pdb) l
    2         _DEBUG=True
    3         def debug_demo(val):
    4                         if _DEBUG == True:
    5                                         import pdb
    6                                         pdb.set_trace()
    7    ->                 if val <= 1600 :
    8                                         print "level 1"
    9                                         print 0
10                         elif val <= 3500 :
11                                         print "level 2"
12                                         print (val - 1600) * 0.05
(Pdb)    
 
左边是行号,右边是代码正文。
 
  监视变量:p 变量名
 
(Pdb) p val
4500
(Pdb)    
 
 单步执行: n
 
-> elif val <= 3500 :
(Pdb) l
    5                                         import pdb
    6                                         pdb.set_trace()
    7                         if val <= 1600 :
    8                                         print "level 1"
    9                                         print 0
10    ->                 elif val <= 3500 :
11                                         print "level 2"
12                                         print (val - 1600) * 0.05
13                         elif val <= 6500 :
14                                         print "level 3"
15                                         print (val - 3500) * 0.10 + (3500-1600) * 0.05
 
 加入断点:b 行号
 
(Pdb) b 14
 
运行到断点: c
 
(Pdb) c
> /*****
-> print "level 3"
(Pdb) l
    9                                         print 0
10                         elif val <= 3500 :
11                                         print "level 2"
12                                         print (val - 1600) * 0.05
13                         elif val <= 6500 :
14 B->                                 print "level 3"
15                                         print (val - 3500) * 0.10 + (3500-1600) * 0.05
16                         else:
17                                         print "level 4"
18                                         print (val - 6500) * 0.20 + (6500-3500) * 0.10 + (3500-1600) * 0.05
19    
 
执行到函数返回前: r
 
(Pdb) r
level 3
195.0
--Return--
> /****()
->None
-> print (val - 3500) * 0.10 + (3500-1600) * 0.05
(Pdb)    
 
说明:
  pdb还有很多其他很多有用的指令,读者可以自行探索。输入h,h 命令。就可以得到命令的详细帮助。
  不过,我个人认为一般无需启动这种调试方法,一般使用日志输出进行调试即可,除非遇到了非常微妙的错误。这时,单步调试的威力便显示出来了。
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