PYTHON 代碼，尤其是別人寫的代碼看不懂。怎麼辦？ 其實PYTHON中也提供了類似於C語言中用於debug 的 gdb。它叫做pdb。結合本人自己的學習，進行簡單的舉例，以做備忘和補償學習。
首先參考資料:
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 代碼爲例子，演示相應的基本命令使用。
local.py 代碼:
#!/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()爲了配合測試，寫了一個假的配置文件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 進行調試和獲取幫助
1、腳本啓動時，即載入pdb 調試信息
python -m pdb scriptfile [arg] #此中情況，程序在代碼的第一行設置了一個斷點
2、更改腳本加入pdb 調試信息
import pdb pdb.set_trace() # 在程序某處設置斷點
OK ,我們這裏爲了圖簡單，就不去更改local.py 源代碼了，直接使用第一種方法去調試
$ 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
從以上結果也可以看出,默認代碼的第一行爲斷點(只是一個假象的斷點，顯示斷點指令是看不到的)，程序停留在此處。
在pdb 狀態下，使用help 指令可以獲取pdb的幫助信息。
二、n(next)
n(next) 輸入的時候，可以執行代碼的下一行。
(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) # 此處爲空白，按了一個回車鍵 > /home/test/python/shadowsocks/shadowsocks/local.py(24)<module>() -> import signal (Pdb) # 此處爲空白，按了一個回車鍵 > /home/test/python/shadowsocks/shadowsocks/local.py(26)<module>() -> sys.path.insert(0, os.path.join(os.path.dirname(__file__), '../')) (Pdb)
注意：
一個很牛的特性是你可以單擊回車鍵來執行以前的命令（在上面的例子中執行的指令爲n）。
三、s(step) 、 b(break) 和 c(continue) 指令
s(step) 輸入的時候，可以進入這行代碼中的相關函數去執行
b num 輸入的時候，是在某行(num)上設置一個斷點。若直接輸入b ，則顯示所有的斷點
本來，打算講s(step)指令和 n(next)指令放到一起，做個比較。不過我更感覺s(step) 指令應該和b(break) 及 c(continue)結合起來一起用，這樣感覺效率上更高。
以實際操作去說話，我想在main()函數上打一個斷點，然後直接走到這個斷點，最後進入main函數。
前提，我知道了 main() 函數位於 72行(函數位於文件中的哪一行，這個靠自己了)
> /home/test/python/shadowsocks/shadowsocks/local.py(18)<module>()
-> from __future__ import absolute_import, division, print_function, \
(Pdb) b 72 # 在72 行設置一個斷點
Breakpoint 1 at /home/test/python/shadowsocks/shadowsocks/local.py:72
(Pdb) b # 顯示所有的斷點
Num Type Disp Enb Where
1 breakpoint keep yes at /home/test/python/shadowsocks/shadowsocks/local.py:72
(Pdb) c # 直接走到這個斷點處
> /home/test/python/shadowsocks/shadowsocks/local.py(72)<module>()
-> main()
(Pdb) s # s ,進入main 函數
--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 移動到下一行
> /home/dexin/python/shadowsocks/shadowsocks/local.py(31)main()
-> shell.check_python()
(Pdb) s # s 進入到 check_python 函數
--Call--
> /home/dexin/python/shadowsocks/shadowsocks/shell.py(35)check_python()
-> def check_python():
(Pdb)以上調試中，用的了 l(list) 指令，這個指令的意思爲顯示代碼。默認什麼參數也沒有的情況下。
顯示當前行上下共11行代碼。
四、clear num 清除先前設置的斷點 ,這裏的num 爲第幾個斷點的意思
(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 # 顯示所有的斷點
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 # 清除第一個斷點
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
這個指令的功能主要用於打印程序中的變量值
(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 # 打印變量值
sys.version_info(major=2, minor=7, micro=6, releaselevel='final', serial=0)六、動態調整變量的值
(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