PYTHON 代码，尤其是别人写的代码看不懂。怎么办？ 其实PYTHON中也提供了类似于C语言中用于debug 的 gdb。它叫做pdb。结合本人自己的学习，进行简单的举例，以做备忘和补偿学习。
首先参考资料:
1、http://web.stanford.edu/class/physics91si/2013/handouts/Pdb_Commands.pdf
2、https://docs.python.org/2/library/pdb.html
以 shadowsocks 的 local.py 代码为例子，演示相应的基本命令使用。
local.py 代码:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright 2012-2015 clowwindy
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
from __future__ import absolute_import, division, print_function, \
with_statement
import sys
import os
import logging
import signal
sys.path.insert(0, os.path.join(os.path.dirname(__file__), '../'))
from shadowsocks import shell, daemon, eventloop, tcprelay, udprelay, asyncdns
def main():
shell.check_python()
# fix py2exe
if hasattr(sys, "frozen") and sys.frozen in \
("windows_exe", "console_exe"):
p = os.path.dirname(os.path.abspath(sys.executable))
os.chdir(p)
config = shell.get_config(True)
daemon.daemon_exec(config)
try:
logging.info("starting local at %s:%d" %
(config['local_address'], config['local_port']))
dns_resolver = asyncdns.DNSResolver()
tcp_server = tcprelay.TCPRelay(config, dns_resolver, True)
udp_server = udprelay.UDPRelay(config, dns_resolver, True)
loop = eventloop.EventLoop()
dns_resolver.add_to_loop(loop)
tcp_server.add_to_loop(loop)
udp_server.add_to_loop(loop)
def handler(signum, _):
logging.warn('received SIGQUIT, doing graceful shutting down..')
tcp_server.close(next_tick=True)
udp_server.close(next_tick=True)
signal.signal(getattr(signal, 'SIGQUIT', signal.SIGTERM), handler)
def int_handler(signum, _):
sys.exit(1)
signal.signal(signal.SIGINT, int_handler)
daemon.set_user(config.get('user', None))
loop.run()
except Exception as e:
shell.print_exception(e)
sys.exit(1)
if __name__ == '__main__':
main()为了配合测试，写了一个假的配置文件config.json:
{
"server":"127.0j.0.1",
"server_port":8388,
"local_port":10808,
"password":"bgt56yhn",
"timeout":600,
"method":null
}一、如何使用pdb 进行调试和获取帮助
1、脚本启动时，即载入pdb 调试信息
python -m pdb scriptfile [arg] #此中情况，程序在代码的第一行设置了一个断点2、更改脚本加入pdb 调试信息
import pdb
pdb.set_trace() # 在程序某处设置断点OK ,我们这里为了图简单，就不去更改local.py 源代码了，直接使用第一种方法去调试
$ python -m pdb local.py -c config.json
> /home/test/python/shadowsocks/shadowsocks/local.py(18)<module>()
-> from __future__ import absolute_import, division, print_function, \
(Pdb) help
Documented commands (type help <topic>):
========================================
EOF bt cont enable jump pp run unt
a c continue exit l q s until
alias cl d h list quit step up
args clear debug help n r tbreak w
b commands disable ignore next restart u whatis
break condition down j p return unalias where
Miscellaneous help topics:
==========================
exec pdb
Undocumented commands:
======================
retval rv从以上结果也可以看出,默认代码的第一行为断点(只是一个假象的断点，显示断点指令是看不到的)，程序停留在此处。
在pdb 状态下，使用help 指令可以获取pdb的帮助信息。
二、n(next)
n(next) 输入的时候，可以执行代码的下一行。
(Pdb) n
> /home/test/python/shadowsocks/shadowsocks/local.py(21)<module>()
-> import sys
(Pdb) n
> /home/test/python/shadowsocks/shadowsocks/local.py(22)<module>()
-> import os
(Pdb) n
> /home/test/python/shadowsocks/shadowsocks/local.py(23)<module>()
-> import logging
(Pdb) # 此处为空白，按了一个回车键
> /home/test/python/shadowsocks/shadowsocks/local.py(24)<module>()
-> import signal
(Pdb) # 此处为空白，按了一个回车键
> /home/test/python/shadowsocks/shadowsocks/local.py(26)<module>()
-> sys.path.insert(0, os.path.join(os.path.dirname(__file__), '../'))
(Pdb)注意：
一个很牛的特性是你可以单击回车键来执行以前的命令（在上面的例子中执行的指令为n）。
三、s(step) 、 b(break) 和 c(continue) 指令
s(step) 输入的时候，可以进入这行代码中的相关函数去执行
b num 输入的时候，是在某行(num)上设置一个断点。若直接输入b ，则显示所有的断点
本来，打算讲s(step)指令和 n(next)指令放到一起，做个比较。不过我更感觉s(step) 指令应该和b(break) 及 c(continue)结合起来一起用，这样感觉效率上更高。
以实际操作去说话，我想在main()函数上打一个断点，然后直接走到这个断点，最后进入main函数。
前提，我知道了 main() 函数位于 72行(函数位于文件中的哪一行，这个靠自己了)
> /home/test/python/shadowsocks/shadowsocks/local.py(18)<module>()
-> from __future__ import absolute_import, division, print_function, \
(Pdb) b 72 # 在72 行设置一个断点
Breakpoint 1 at /home/test/python/shadowsocks/shadowsocks/local.py:72
(Pdb) b # 显示所有的断点
Num Type Disp Enb Where
1 breakpoint keep yes at /home/test/python/shadowsocks/shadowsocks/local.py:72
(Pdb) c # 直接走到这个断点处
> /home/test/python/shadowsocks/shadowsocks/local.py(72)<module>()
-> main()
(Pdb) s # s ,进入main 函数
--Call--
> /home/dexin/python/shadowsocks/shadowsocks/local.py(30)main()
-> def main():
(Pdb) l
25
26 sys.path.insert(0, os.path.join(os.path.dirname(__file__), '../'))
27 from shadowsocks import shell, daemon, eventloop, tcprelay, udprelay, asyncdns
28
29
30 -> def main():
31 shell.check_python()
32
33 # fix py2exe
34 if hasattr(sys, "frozen") and sys.frozen in \
35 ("windows_exe", "console_exe"):
(Pdb) n # n 移动到下一行
> /home/dexin/python/shadowsocks/shadowsocks/local.py(31)main()
-> shell.check_python()
(Pdb) s # s 进入到 check_python 函数
--Call--
> /home/dexin/python/shadowsocks/shadowsocks/shell.py(35)check_python()
-> def check_python():
(Pdb)以上调试中，用的了 l(list) 指令，这个指令的意思为显示代码。默认什么参数也没有的情况下。
显示当前行上下共11行代码。
四、clear num 清除先前设置的断点 ,这里的num 为第几个断点的意思
(Pdb) b 34
Breakpoint 1 at /home/test/python/shadowsocks/shadowsocks/local.py:34
(Pdb) b
Num Type Disp Enb Where
1 breakpoint keep yes at /home/test/python/shadowsocks/shadowsocks/local.py:34
(Pdb) l
36 p = os.path.dirname(os.path.abspath(sys.executable))
37 os.chdir(p)
38
39 config = shell.get_config(True)
40
41 daemon.daemon_exec(config)
42
43 try:
44 logging.info("starting local at %s:%d" %
45 (config['local_address'], config['local_port']))
46
(Pdb) b 41
Breakpoint 2 at /home/dexin/python/shadowsocks/shadowsocks/local.py:41
(Pdb) b # 显示所有的断点
Num Type Disp Enb Where
1 breakpoint keep yes at /home/dexin/python/shadowsocks/shadowsocks/local.py:34
2 breakpoint keep yes at /home/dexin/python/shadowsocks/shadowsocks/local.py:41
(Pdb) clear 1 # 清除第一个断点
Deleted breakpoint 1
(Pdb) b
Num Type Disp Enb Where
2 breakpoint keep yes at /home/dexin/python/shadowsocks/shadowsocks/local.py:41
(Pdb)五、p(print) 打印
这个指令的功能主要用于打印程序中的变量值
(Pdb) n
> /home/test/python/shadowsocks/shadowsocks/shell.py(37)check_python()
-> if info[0] == 2 and not info[1] >= 6:
(Pdb) l
32 verbose = 0
33
34
35 def check_python():
36 info = sys.version_info
37 -> if info[0] == 2 and not info[1] >= 6:
38 print('Python 2.6+ required')
39 sys.exit(1)
40 elif info[0] == 3 and not info[1] >= 3:
41 print('Python 3.3+ required')
42 sys.exit(1)
(Pdb) p info # 打印变量值
sys.version_info(major=2, minor=7, micro=6, releaselevel='final', serial=0)六、动态调整变量的值
(Pdb) n
> /home/test/python/shadowsocks/shadowsocks/shell.py(37)check_python()
-> if info[0] == 2 and not info[1] >= 6:
(Pdb) l
32 verbose = 0
33
34
35 def check_python():
36 info = sys.version_info
37 -> if info[0] == 2 and not info[1] >= 6:
38 print('Python 2.6+ required')
39 sys.exit(1)
40 elif info[0] == 3 and not info[1] >= 3:
41 print('Python 3.3+ required')
42 sys.exit(1)
(Pdb) p info
sys.version_info(major=2, minor=7, micro=6, releaselevel='final', serial=0)
(Pdb) info = (11,22,33)
(Pdb) p info
(11, 22, 33)七、q(quit)退出
(Pdb) quit
