python pdb模块

参考文件http://pythonconquerstheuniverse.wordpress.com/category/Python-debugger/

翻译不是一一对应

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

def test_debugger(some_int):

    print "start some_int>>", some_int

    return_int = 10 / some_int

    print "end some_int>>", some_int

    return return_int

if __name__ == "__main__":

    pdb.run("test_debugger(0)")

`pdb.runeval(expression[,globals[, locals]])`

pdb.runeval() is identical to pdb.run(), exceptthat pdb.runeval() returns the value of the evaluated stringexpression:

#!/usr/bin/env python

import pdb

def test_debugger(some_int):

    print "start some_int>>", some_int

    return_int = 10 / some_int

    print "end some_int>>", some_int

    return return_int

if __name__ == "__main__":

    pdb.runeval("test_debugger(0)")

`pdb.runcall(function[,argument, ...])`

pdb.runcall() calls the specified function andpasses any specified arguments to it:

#!/usr/bin/env python

import pdb

def test_debugger(some_int):

    print "start some_int>>", some_int

    return_int = 10 / some_int

    print "end some_int>>", some_int

    return return_int

if __name__ == "__main__":

    pdb.runcall(test_debugger, 0)

`pdb.set_trace()`

pdb.set_trace() drops the code into the debugger when executionhits it:

#!/usr/bin/env python

import pdb

def test_debugger(some_int):

    pdb.set_trace()

    print "start some_int>>", some_int

    return_int = 10 / some_int

    print "end some_int>>", some_int

    return return_int

if __name__ == "__main__":

    test_debugger(0)

`pdb.post_mortem(traceback)`

pdb.post_mortem() performs postmortem debugging of thespecified traceback:

#!/usr/bin/env python

import pdb

def test_debugger(some_int):

    print "start some_int>>", some_int

    return_int = 10 / some_int

    print "end some_int>>", some_int

    return return_int

if __name__ == "__main__":

    try:

        test_debugger(0)

    except:

        import sys

        tb = sys.exc_info()[2]

        pdb.post_mortem(tb)

`pdb.pm()`

pdb.pm() performs postmortem debugging of the tracebackcontained in sys.last_traceback:

#!/usr/bin/env python

import pdb

import sys

def test_debugger(some_int):

    print "start some_int>>", some_int

    return_int = 10 / some_int

    print "end some_int>>", some_int

    return return_int

def do_debugger(type, value, tb):

    pdb.pm()

if __name__ == "__main__":

    sys.excepthook = do_debugger

    test_debugger(0)

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