Python代碼調試

文章目錄

• 1.print輸出
• 2.logging模組

　　原來不怎麼喜歡調試，寫的程式大了，感覺調試也是很有必要的，簡單總結一下幾種常用的調試方式

1.print輸出

　　不要小看print輸出，有時候，或許這是最快的方式。通過print將某個變數的值輸出，再和預期的值進行比較，有問題的話再去分析源碼看看哪裡有錯誤。

2.logging模組

　　這個模組比較強大，也很有用，完全可以替代print。logging模組可以定義記錄層級，包括NOTSET < DEBUG < INFO < WARNING < ERROR < CRITICAL這幾個層級，通過設定可以輸出某個層級以上的日誌，可以選擇將日誌儲存到檔案或者在螢幕輸出。具體用法可以參考python手冊

3.用bpython編寫代碼

　　這個編輯器的優點是寫完一行代碼之後立即執行，然後我們能立即看到結果，出現問題可以及時撤銷代碼，編寫完成可以將代碼儲存。代碼提示功能也挺強大的。

4.用python -i來執行代碼

　　這樣執行之後，程式並沒有立即退出。而是開啟一個python互動式命令列介面，在這裡我們可以執行一些命令，比如 dir() 來查看變數和函數，直接輸入變數名我們就能查看變數的值。如果程式異常退出的話，也會保留“現場”，我們可以從現場來分析，找到錯誤。

5.pdb調試

　　最後講這個神器。

　　看了一下官方文檔，pdb模組是用bdp模組和cmd模組來實現的。實作類別似pdb的功能。

　　使用這個模組的話簡單的方法就是設定斷點，先倒入pdb模組，然後在需要停下的地方執行pdb.set_trace()命令，這樣程式執行到這個命令的時候就會停下來，然後我們就能輸入一些pdb命令來進行調試了。可以逐步執行，繼續執行，可以查看變數的值，可以執行一些語句，可以顯示將要執行的代碼塊，可以讓程式跳轉，執行另外的語句。

　　詳細的命令可以參考官方文檔：

h(elp) [command]Without argument, print the list of available commands. With a command as argument, print help about that command. help pdb displays the full documentation file; if the environment variable PAGER is defined, the file is piped through that command instead. Since thecommand argument must be an identifier, help exec must be entered to get help on the ! command.w(here)Print a stack trace, with the most recent frame at the bottom. An arrow indicates the current frame, which determines the context of most commands.d(own)Move the current frame one level down in the stack trace (to a newer frame).u(p)Move the current frame one level up in the stack trace (to an older frame).b(reak) [[filename:]lineno | function[, condition]]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.tbreak [[filename:]lineno | function[, condition]]Temporary breakpoint, which is removed automatically when it is first hit. The arguments are the same as break.cl(ear) [filename:lineno | bpnumber [bpnumber ...]]With a filename:lineno argument, clear all the breakpoints at this line. With a space separated list of breakpoint numbers, clear those breakpoints. Without argument, clear all breaks (but first ask confirmation).disable [bpnumber [bpnumber ...]]Disables the breakpoints given as a space separated list of breakpoint numbers. Disabling a breakpoint means it cannot cause the program to stop execution, but unlike clearing a breakpoint, it remains in the list of breakpoints and can be (re-)enabled.enable [bpnumber [bpnumber ...]]Enables the breakpoints specified.ignore bpnumber [count]Sets the ignore count for the given breakpoint number. If count is omitted, the ignore count is set to 0. A breakpoint becomes active when the ignore count is zero. When non-zero, the count is decremented each time the breakpoint is reached and the breakpoint is not disabled and any associated condition evaluates to true.condition bpnumber [condition]Condition is an expression which must evaluate to true before the breakpoint is honored. If condition is absent, any existing condition is removed; i.e., the breakpoint is made unconditional.commands [bpnumber]Specify a list of commands for breakpoint number 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.With no 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.New in version 2.5.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 between next and step is that stepstops inside a called function, while next 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) linenoSet 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 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 expressionEvaluate 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 Python print statement.pp expressionLike the p command, except the value of the expression is pretty-printed using the pprint module.alias [name [command]]Creates an alias called name that executes command. The command must 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 selfalias ps pi selfunalias nameDeletes the specified alias.[!]statementExecute the (one-line) statement 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)run [args ...]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”.New in version 2.6.q(uit)Quit from the debugger. The program being executed is aborted.