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Python debug 模块之pdb–(一)

2014年12月22日

Python debug 模块之pdb–(一)
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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