The PDB module in Python

PYTHON code, especially code written by someone else, doesn't understand. What to do? In fact Python also provides a similar to the C language for debug gdb. It's called the PDB. Combined with my own study, a simple example, to do memo and compensatory learning.

First, reference:

1, Http://web.stanford.edu/class/physics91si/2013/handouts/Pdb_Commands.pdf

2, https://docs.python.org/2/library/pdb.html

Use Shadowsocks's local.py code as an example to demonstrate the corresponding basic command.

local.py Code:

#!/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&Nbsp;and limitations# under the license.from __future__ import absolute_ Import, division, print_function,     with_statementimport sysimport  osimport loggingimport signalsys.path.insert (0, os.path.join (Os.path.dirname (__file__),   '. /')) From shadowsocks import shell, daemon, eventloop, tcprelay, udprelay,  asyncdnsdef 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))       &Nbsp; loop.run ()     except Exception as e:         shell.print_exception (E)         sys.exit (1) if  __name__ ==  ' __main__ ':     main ()

To match the test, write a fake profile Config.json:

{"Server": "127.0j.0.1", "Server_port": 8388, "Local_port": 10808, "password": "Bgt56yhn", "Timeout": 600, " Method ": null}

I. How to debug and get help using the PDB

1. When the script starts, it loads the PDB debug information

python-m pdb ScriptFile [ARG] #此中情况, the program sets a breakpoint on the first line of the code

2. Change script to add PDB debug information

Import Pdbpdb.set_trace () # Set a breakpoint somewhere in the program

OK, we are here for simple diagram, do not change the local.py source code, directly using the first method to debug

 $ python -m pdb local.py  -c config.json> /home/test/python/ shadowsocks/shadowsocks/local.py (+) <module> ()-> from __future__ import absolute_ import, division, print_function,  (Pdb)  helpDocumented 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         whatisbreak  condition  down      j        p     return   unalias   where miscellaneous help topics:==========================exec  pdbundocumented  commands:======================retval  rv 

As can be seen from the above results, the default code of the first behavior breakpoint (just a false breakpoint, the Display breakpoint command is not visible), the program stays here.

In the PDB state, use the Help directive to obtain the PDB's assistance.

Second, n (next)

When n (next) is entered, the next line of code can be executed.

(PDB) n>/home/test/python/shadowsocks/shadowsocks/local.py <module> () import sys (PDB) n>/home/ test/python/shadowsocks/shadowsocks/local.py (<module>), import OS (Pdb) n>/home/test/python/ shadowsocks/shadowsocks/local.py (<module>), Import logging (Pdb) # Here is a blank, press a enter >/HOME/TEST/PYT hon/shadowsocks/shadowsocks/local.py (<module>), import Signal (PDB) # Here is a blank, press a enter >/home/test/p ython/shadowsocks/shadowsocks/local.py (+) <module> () sys.path.insert (0, Os.path.join (os.path.dirname ( __file__), '. /')) (PDB)

Attention:
A very bull feature is that you can click the ENTER key to execute the previous command (the command executed in the example above is N).

Third, S (step), B (Break) and C (continue) directives

s (step) input, you can enter the relevant function in this line of code to execute

When B num is entered, a breakpoint is set on a line (num). If you enter B directly, all breakpoints are displayed

Originally, intended to talk about the s (step) instruction and the n (next) instructions put together, make a comparison. But I feel more like the S (step) directive should be combined with B (break) and C (continue) to make it feel more efficient.

To actually speak, I want to hit a breakpoint on the main () function, then go straight to the breakpoint and finally enter the main function.

The premise is, I know the main () function is in line 72 (which line of the function is in the file, this is on its own)

> /home/test/python/shadowsocks/shadowsocks/local.py (+) <module> ()-> from __future_ _ import absolute_import, division, print_function,  (PDB)  b 72      #  set a breakpoint on the 72  line breakpoint 1 at /home/test/python/shadowsocks/ shadowsocks/local.py:72 (PDB)  b        #  Show All Breakpoints Num type          Disp Enb   Where1    breakpoint   keep yes   at /home/test/python/shadowsocks/shadowsocks/ local.py:72 (Pdb)  c        #  go straight to this breakpoint > /home/test/ python/shadowsocks/shadowsocks/local.py <module> ()-> main () (PDB)  s         # s , enter the main  function--call--> /home/dexin/python/shadowsocks/ shadowsocks/local.py (+) 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   moves to the next line > /home/dexin/python/shadowsocks/shadowsocks/local.py () main ()-> shell.check_ Python () (Pdb)  s         # s  go to  check_python   function--call--> /home/dexin/python/shadowsocks/shadowsocks/shell.py (+) Check_python ()-> def  check_python ():(Pdb)

In the above debugging, the use of the L (list) instruction, the meaning of this command is to display the code. The default is not what parameters are in the case.

Displays a total of 11 lines of code up and down the current line.

Clear Num Clears the previously set breakpoint, where Num is the meaning of the first breakpoint

(PDB)  B 34BREAKPOINT 1 AT /HOME/TEST/PYTHON/SHADOWSOCKS/SHADOWSOCKS/LOCAL.PY:34 (PDB)  bNum Type         Disp Enb    where1   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 41breakpoint 2 at /home/dexin/python/shadowsocks/ Shadowsocks/local.py:41 (PDB)  b         #  Show all Breakpoints num  Type         Disp Enb   Where1    breakpoint   keep yes   at /home/dexin/python/shadowsocks/ shadowsocks/local.py:342   breakpoint   keep yes   at / Home/dexin/python/shadowsocks/shAdowsocks/local.py:41 (PDB)  clear 1    #  Clear First breakpoint Deleted breakpoint  1 (PDB)  bNum Type         Disp Enb    where2   breakpoint   keep yes   at /home/ Dexin/python/shadowsocks/shadowsocks/local.py:41 (PDB)

V, p (print) printing

The function of this instruction is mainly used to print the variable values in the program.

(Pdb)  n> /home/test/python/shadowsocks/shadowsocks/shell.py (PNS) 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  #   Print Variable value sys.version_info (major=2, minor=7, micro=6, releaselevel= ' final ',  serial=0)

Vi. dynamic adjustment of variable values

(Pdb)  n> /home/test/python/shadowsocks/shadowsocks/shell.py (PNS) 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 infosys.version_info ( Major=2, minor=7, micro=6, releaselevel= ' final ',  serial=0) (Pdb)  info =  ( 11,22,33) (Pdb)  p info (11, 22, 33)

Seven, Q (quit) exit

(PDB) quit

This article is from the "Learning Notes" blog, so be sure to keep this source http://unixman.blog.51cto.com/10163040/1663867

The PDB module in Python