源代码： Lib/pdb.py
模块 pdb 为 Python 程序定义交互源代码调试器。它支持在源代码行级别设置 (条件) 断点和单步执行、审查堆栈帧、列出源代码、及在任何堆栈帧上下文中评估任意 Python 代码。它支持事后调试，且还可以在程序控制下被调用。
The debugger is extensible — it is actually defined as the class Pdb 。这目前未文档化，但通过阅读源代码很容易理解。扩展接口使用模块 bdb and cmd .
调试器提示为 (Pdb) 。在调试器控制下运行程序的典型用法：
>>> import pdb >>> import mymodule >>> pdb.run('mymodule.test()') > <string>(0)?() (Pdb) continue > <string>(1)?() (Pdb) continue NameError: 'spam' > <string>(1)?() (Pdb)
pdb.py 还可以援引作为调试其它脚本的脚本。例如：
python -m pdb myscript.py
When invoked as a script, pdb will automatically enter post-mortem debugging if the program being debugged exits abnormally. After post-mortem debugging (or after normal exit of the program), pdb will restart the program. Automatic restarting preserves pdb’s state (such as breakpoints) and in most cases is more useful than quitting the debugger upon program’s exit.
New in version 2.4: Restarting post-mortem behavior added.
The typical usage to break into the debugger from a running program is to insert
import pdb; pdb.set_trace()
at the location you want to break into the debugger. You can then step through the code following this statement, and continue running without the debugger using the c 命令。
审查崩溃程序的典型用法：
>>> import pdb >>> import mymodule >>> mymodule.test() Traceback (most recent call last): File "<stdin>", line 1, in ? File "./mymodule.py", line 4, in test test2() File "./mymodule.py", line 3, in test2 print spam NameError: spam >>> pdb.pm() > ./mymodule.py(3)test2() -> print spam (Pdb) Traceback (most recent call last): File "<stdin>", line 1, in ? File "./mymodule.py", line 4, in test test2() File "./mymodule.py", line 3, in test2 print spam NameError: spam
The module defines the following functions; each enters the debugger in a slightly different way:
执行 语句 (given as a string) under debugger control. The debugger prompt appears before any code is executed; you can set breakpoints and type continue , or you can step through the statement using step or next (all these commands are explained below). The optional globals and locals arguments specify the environment in which the code is executed; by default the dictionary of the module __main__ is used. (See the explanation of the exec statement or the eval() built-in function.)
评估 表达式 (given as a string) under debugger control. When runeval() returns, it returns the value of the expression. Otherwise this function is similar to run() .
调用 function (a function or method object, not a string) with the given arguments. When runcall() returns, it returns whatever the function call returned. The debugger prompt appears as soon as the function is entered.
Enter the debugger at the calling stack frame. This is useful to hard-code a breakpoint at a given point in a program, even if the code is not otherwise being debugged (e.g. when an assertion fails).
Enter post-mortem debugging of the given traceback 对象。若无 traceback is given, it uses the one of the exception that is currently being handled (an exception must be being handled if the default is to be used).
Enter post-mortem debugging of the traceback found in sys.last_traceback .
The run* 函数和 set_trace() 是别名对于实例化的 Pdb 类且调用同名方法。若想要访问进一步特征，自己必须这样做：
Pdb 是调试器类。
The completekey , stdin and stdout 自变量会被传递给底层 cmd.Cmd 类；见这里的描述。
The skip argument, if given, must be an iterable of glob-style module name patterns. The debugger will not step into frames that originate in a module that matches one of these patterns. [1]
范例调用启用跟踪采用 skip :
import pdb; pdb.Pdb(skip=['django.*']).set_trace()
New in version 2.7: The skip 自变量。
The debugger recognizes the following commands. Most commands can be abbreviated to one or two letters; e.g. h(elp) means that either h or help can be used to enter the help command (but not he or hel , nor H or 帮助 or HELP ). Arguments to commands must be separated by whitespace (spaces or tabs). Optional arguments are enclosed in square brackets ( [] ) in the command syntax; the square brackets must not be typed. Alternatives in the command syntax are separated by a vertical bar ( | ).
Entering a blank line repeats the last command entered. Exception: if the last command was a list command, the next 11 lines are listed.
Commands that the debugger doesn’t recognize are assumed to be Python statements and are executed in the context of the program being debugged. Python statements can also be prefixed with an exclamation point ( ! ). This is a powerful way to inspect the program being debugged; it is even possible to change a variable or call a function. When an exception occurs in such a statement, the exception name is printed but the debugger’s state is not changed.
Multiple commands may be entered on a single line, separated by ;; 。(单 ; is not used as it is the separator for multiple commands in a line that is passed to the Python parser.) No intelligence is applied to separating the commands; the input is split at the first ;; pair, even if it is in the middle of a quoted string.
The debugger supports aliases. Aliases can have parameters which allows one a certain level of adaptability to the context under examination.
若文件 .pdbrc exists in the user’s home directory or in the current directory, it is read in and executed as if it had been typed at the debugger prompt. This is particularly useful for aliases. If both files exist, the one in the home directory is read first and aliases defined there can be overridden by the local file.
With a lineno argument, set a break there in the current file. With a function argument, set a break at the first executable statement within that function. The line number may be prefixed with a filename and a colon, to specify a breakpoint in another file (probably one that hasn’t been loaded yet). The file is searched on sys.path . Note that each breakpoint is assigned a number to which all the other breakpoint commands refer.
If a second argument is present, it is an expression which must evaluate to true before the breakpoint is honored.
Without argument, list all breaks, including for each breakpoint, the number of times that breakpoint has been hit, the current ignore count, and the associated condition if any.
指定命令列表为断点编号 bpnumber . The commands themselves appear on the following lines. Type a line containing just ‘end’ to terminate the commands. 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.
不带 bpnumber argument, commands refers to the last breakpoint set.
You can use breakpoint commands to start your program up again. Simply use the continue command, or step, or any other command that resumes execution.
Specifying any command resuming execution (currently continue, step, next, return, jump, quit and their abbreviations) terminates the command list (as if that command was immediately followed by end). This is because any time you resume execution (even with a simple next or step), you may encounter another breakpoint–which could have its own command list, leading to ambiguities about which list to execute.
If you use the ‘silent’ command in the command list, the usual message about stopping at a breakpoint is not printed. This may be desirable for breakpoints that are to print a specific message and then continue. If none of the other commands print anything, you see no sign that the breakpoint was reached.
2.5 版新增。
Continue execution until the line with the line number greater than the current one is reached or when returning from current frame.
2.6 版新增。
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 a for loop or out of a finally 子句。
评估 表达式 in the current context and print its value.
注意
print can also be used, but is not a debugger command — this executes the Python print 语句。
Creates an alias called name 执行 命令 。命令必须 not be enclosed in quotes. Replaceable parameters can be indicated by %1 , %2 , and so on, while %* is replaced by all the parameters. If no command is given, the current alias for name is shown. If no arguments are given, all aliases are listed.
Aliases may be nested and can contain anything that can be legally typed at the pdb prompt. Note that internal pdb commands can be overridden by aliases. Such a command is then hidden until the alias is removed. Aliasing is recursively applied to the first word of the command line; all other words in the line are left alone.
As an example, here are two useful aliases (especially when placed in the .pdbrc file):
#Print instance variables (usage "pi classInst")
alias pi for k in %1.__dict__.keys(): print "%1.",k,"=",%1.__dict__[k]
#Print instance variables in self
alias ps pi self
执行 (1 行) 语句 in the context of the current stack frame. The exclamation point can be omitted unless the first word of the statement resembles a debugger command. To set a global variable, you can prefix the assignment command with a global command on the same line, e.g.:
(Pdb) global list_options; list_options = ['-l']
(Pdb)
Restart the debugged Python program. If an argument is supplied, it is split with “shlex” and the result is used as the new sys.argv. History, breakpoints, actions and debugger options are preserved. “restart” is an alias for “run”.
2.6 版新增。
脚注
| [1] | Whether a frame is considered to originate in a certain module is determined by the __name__ in the frame globals. |