python pdb小结

Debug功能对于developer是非常重要的，python提供了相应的模块pdb让你可以在用文本编辑器写脚本的情况下进行debug. pdb是python debugger的简称。
常用的一些命令如下：
命令用途
break 或 b 设置断点
continue 或 c 继续执行程序
list 或 l 查看当前行的代码段
step 或 s 进入函数
return 或 r 执行代码直到从当前函数返回
exit 或 q 中止并退出
next 或 n 执行下一行
pp 打印变量的值
help 帮助
开始介绍如何使用pdb。
使用的测试代码1： epdb1.py
import pdb
a = "aaa"
pdb.set_trace()
b = "bbb"
c = "ccc"
final = a + b + c
print final
关于set_trace()
pdb.set_trace()
Enter the debugger at the calling stack frame. This is useful to hard-code abreakpoint at a given point in a program, even if the code is not otherwisebeing debugged (e.g. when an assertion fails).
1 开始调试：
[root@rcc-pok-idg-2255 ~]# python epdb1.py
> /root/epdb1.py(4)?()
-> b = "bbb"
(Pdb) n
> /root/epdb1.py(5)?()
-> c = "ccc"
(Pdb)
> /root/epdb1.py(6)?()
-> final = a + b + c
(Pdb) list
1 import pdb
2 a = "aaa"
3 pdb.set_trace()
4 b = "bbb"
5 c = "ccc"
6 -> final = a + b + c
7 print final
[EOF]
(Pdb)
[EOF]
(Pdb) n
> /root/epdb1.py(7)?()
-> print final
(Pdb)
使用n+enter表示执行当前的statement，在第一次按下了n+enter之后可以直接按enter表示重复执行上一条debug命令。
If you press ENTER without entering anything, pdb will re-execute the last command that you gave it.

quit或者q可以退出当前的debug，但是quit会以一种非常粗鲁的方式退出程序，直接crash
[root@rcc-pok-idg-2255 ~]# python epdb1.py
> /root/epdb1.py(4)?()
-> b = "bbb"
(Pdb) n
> /root/epdb1.py(5)?()
-> c = "ccc"
(Pdb) q
Traceback (most recent call last):
File "epdb1.py", line 5, in ?
c = "ccc"
File "epdb1.py", line 5, in ?
c = "ccc"
File "/usr/lib64/python2.4/bdb.py", line 48, in trace_dispatch
return self.dispatch_line(frame)
File "/usr/lib64/python2.4/bdb.py", line 67, in dispatch_line
if self.quitting: raise BdbQuit
bdb.BdbQuit

在使用过程中打印变量的值，可以直接使用p加上变量名，但是需要注意的是打印仅仅在当前的statement已经被执行了之后才能看到具体的值，否则会报 NameError: <exceptions.NameError 。。> 错误。
[root@rcc-pok-idg-2255 ~]# python epdb1.py
> /root/epdb1.py(4)?()
-> b = "bbb"
(Pdb) n
> /root/epdb1.py(5)?()
-> c = "ccc"
(Pdb) p b
'bbb'
(Pdb)
'bbb'
(Pdb) n
> /root/epdb1.py(6)?()
-> final = a + b + c
(Pdb) p c
'ccc'
(Pdb) p final
*** NameError: <exceptions.NameError instance at 0x1551b710>
(Pdb) n
> /root/epdb1.py(7)?()
-> print final
(Pdb) p final
'aaabbbccc'
(Pdb)

使用c可以停止当前的debug使得程序继续执行。如果在下面的程序中继续有set_statement()的申明，则又会重新进入到debug的状态。
[root@rcc-pok-idg-2255 ~]# python epdb1.py
> /root/epdb1.py(4)?()
-> b = "bbb"
(Pdb) n
> /root/epdb1.py(5)?()
-> c = "ccc"
(Pdb) c
aaabbbccc

可以在代码print final之前再加上set_trace()验证。

如果代码过程，在debug的时候不一定能记住当前的代码快，则可以通过使用list或者l命令在显示。list会用箭头->指向当前debug的语句
[root@rcc-pok-idg-2255 ~]# python epdb1.py
> /root/epdb1.py(4)?()
-> b = "bbb"
(Pdb) list
1 import pdb
2 a = "aaa"
3 pdb.set_trace()
4 -> b = "bbb"
5 c = "ccc"
6 final = a + b + c
7 pdb.set_trace()
8 print final
[EOF]
(Pdb) c
> /root/epdb1.py(8)?()
-> print final
(Pdb) list
3 pdb.set_trace()
4 b = "bbb"
5 c = "ccc"
6 final = a + b + c
7 pdb.set_trace()
8 -> print final
[EOF]
(Pdb)
对于使用函数的情况下进行debug：
epdb2.py --import pdb

def combine(s1,s2): # define subroutine combine, which...
s3 = s1 + s2 + s1 # sandwiches s2 between copies of s1, ...
s3 = '"' + s3 +'"' # encloses it in double quotes,...
return s3 # and returns it.

a = "aaa"
pdb.set_trace()
b = "bbb"
c = "ccc"
final = combine(a,b)
print final

如果直接使用n进行debug则到final=combine这句的时候会将其当做普通的赋值语句处理，进入到print final。如果想要对函数进行debug如何处理？可以直接使用s进入函数块。
[root@rcc-pok-idg-2255 ~]# python epdb2.py
> /root/epdb2.py(10)?()
-> b = "bbb"
(Pdb) n
> /root/epdb2.py(11)?()
-> c = "ccc"
(Pdb) n
> /root/epdb2.py(12)?()
-> final = combine(a,b)
(Pdb) s
--Call--
> /root/epdb2.py(3)combine()
-> def combine(s1,s2): # define subroutine combine, which...
(Pdb) n
> /root/epdb2.py(4)combine()
-> s3 = s1 + s2 + s1 # sandwiches s2 between copies of s1, ...
(Pdb) list
1 import pdb
2
3 def combine(s1,s2): # define subroutine combine, which...
4 -> s3 = s1 + s2 + s1 # sandwiches s2 between copies of s1, ...
5 s3 = '"' + s3 +'"' # encloses it in double quotes,...
6 return s3 # and returns it.
7
8 a = "aaa"
9 pdb.set_trace()
10 b = "bbb"
11 c = "ccc"
(Pdb) n
> /root/epdb2.py(5)combine()
-> s3 = '"' + s3 +'"' # encloses it in double quotes,...
(Pdb) n
> /root/epdb2.py(6)combine()
-> return s3 # and returns it.
(Pdb) n
--Return--
> /root/epdb2.py(6)combine()->'"aaabbbaaa"'
-> return s3 # and returns it.
(Pdb) n
> /root/epdb2.py(13)?()
-> print final
(Pdb)

如果不想在函数里单步调试可以在断点出直接按r退出到调用的地方。

在调试的时候动态改变值。注意下面有个错误，原因是b已经被赋值了，如果想重新改变b的赋值，则应该使用！b
[root@rcc-pok-idg-2255 ~]# python epdb2.py
> /root/epdb2.py(10)?()
-> b = "bbb"
(Pdb) var = "1234"
(Pdb) b = "avfe"
*** The specified object '= "avfe"' is not a function
or was not found along sys.path.
(Pdb) !b="afdfd"
(Pdb)

再贴一篇好文章：http://onlamp.com/pub/a/python/2005/09/01/debugger.html?page=1
Debugger Module Contents
The pdb module contains the debugger. pdb containsone class, Pdb, which inherits from bdb.Bdb. Thedebugger documentation mentions six functions, which create an interactivedebugging session:
pdb.run(statement[, globals[, locals]])
pdb.runeval(expression[, globals[, locals]])
pdb.runcall(function[, argument, ...])
pdb.set_trace()
pdb.post_mortem(traceback)
pdb.pm()
All six functions provide a slightly different mechanism for dropping a userinto the debugger.
pdb.run(statement[, globals[, locals]])
pdb.run() executes the string statement under thedebugger's control. Global and local dictionaries are optional parameters:
#!/usr/bin/env python

import pdb