python学习一：软件版本选择以及代码调试初探

开始学习python了，争取每天玩一点，写下点心得。

1. 版本选择

官网下载了python 3.3的win安装程序并安装，写了如下简单的测试程序，想看看idle debugger的功能。

CH_TYPE = "ch"
EN_TYPE = "en"
g_name_type = "ch"  # ch / en
g_first_name = "hang"

def PrintFullName():
global g_name_type
global g_first_name
last_name = "Zhang"

if g_name_type == CH_TYPE:
print "full name: %s.%s" % (last_name, g_first_name)

if __name__ == "__main__":
PrintFullName()

未曾想，在

print "full name: %s.%s" % (last_name, g_first_name)

一行报语法错误，search后，发现原来python 2和3有很大差异，从python3.0开始，print由2中的一个statement变为3中的print（）函数，查看3.3的手册，也学会了print函数的使用。那究竟是使用最新的python3还是使用python2呢？

python的网站上有如下一篇文章：
http://wiki.python.org/moin/Python2orPython3
就目前来看，为了获得更多第三方python库的支持，学习python2会更有利于我。所以我重新安装了python2.7.5

2. idle debugger

在idle中勾选debugger后，会弹出debug control窗口。

窗口中会显示stack中当前函数的globals和locals，以及运行到哪一行代码。

左上角的五个控制按钮的功能：Go，程序运行完毕；Step，程序运行单行，并进入函数；Over，程序运行单行，但不进入函数内部；Out，程序运行直到当前函数返回；Quit，程序退出。

同时，可以在程序中单击右键设定breakpoint。

3. pdb

python还可以使用pdb这个module来进行调试，在python的手册中可以索引到pdb模块的教程。

import pdb

CH_TYPE = "ch"
EN_TYPE = "en"
g_name_type = "ch"  # ch / en
g_first_name = "hang"

def PrintFullName():
pdb.set_trace()
global g_name_type
global g_first_name
last_name = "Zhang"

if g_name_type == CH_TYPE:
print "full name: %s.%s" % (last_name, g_first_name)

if __name__ == "__main__":
PrintFullName()

代码中引入pdb，并且在开始debug处调用pdb.set_trace()函数。

这里对几个命令进行了学习：

h(elp) [command]查看某个命令的帮助

w(here) 显示目前的stack信息

d(own) 进入下一个函数栈u(p) 进入上一个函数栈b(reak) [[filename:]lineno |
function[, condition]]设定断点，filename应该在sys.path路径下tbreak [[filename:]lineno |
function[, condition]]设定临时断点cl(ear) [filename:lineno | bpnumber [bpnumber ...]]清楚断点disable [bpnumber [bpnumber ...]]断点失效enable [bpnumber [bpnumber ...]]断点生效ignore bpnumber [count]设置断点失效count次
condition bpnumber [condition] 条件表达式为真，则断点生效；表达式为空，则所有条件被移除

commands [bpnumber]到达断点时候，执行相应命令，以end为结尾

An example:

(Pdb) commands 1
(com) print some_variable
(com) end
(Pdb)

To remove all commands from a breakpoint, type commands and follow it immediately with end; that is, give no commands.

With no bpnumber argument, commands refers to the last breakpoint set.

s(tep) Execute the current line, stop at the first possible occasion (either in a function that is called or on the next line in the current function).n(ext) Continue execution until the next line in the current function is reached or it returns. (The difference betweennext andstep is thatstep
stops inside a called function, whilenext executes called functions at (nearly) full speed, only stopping at the next line in the current function.)unt(il)
Continue execution until the line with the line number greater than the current one is reached or when returning from current frame.
New in version 2.6.
r(eturn) Continue execution until the current function returns.c(ont(inue)) Continue execution, only stop when a breakpoint is encountered.j(ump) lineno
Set the next line that will be executed. Only available in the bottom-most frame. This lets you jump back and execute code again, or jump forward to skip code that you don’t want to run.
It should be noted that not all jumps are allowed — for instance it is not possible to jump into the middle of afor
loop or out of afinally clause.
l(ist) [first[, last]]
List source code for the current file. Without arguments, list 11 lines around the current line or continue the previous listing. With one argument, list 11 lines around at that line. With two arguments, list the given range;
if the second argument is less than the first, it is interpreted as a count.
a(rgs) Print the argument list of the current function.p expression
Evaluate the expression in the current context and print its value.

Note
print can also be used, but is not a debugger command — this executes the Pythonprint
statement.

pp expression Like the p command, except the value of the expression is pretty-printed using thepprint
module.