使用PDB调试Python程序

 

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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