Mercurial > cpython-lru_cache-weakref
annotate Doc/lib/libpdb.tex @ 4566:6403c94de50d legacy-trunk
Added safeguard against failure in __del__.
| author | Guido van Rossum <guido@python.org> |
|---|---|
| date | Wed, 27 Nov 1996 19:39:58 +0000 |
| parents | 175671cc21d8 |
| children | d5911ca8d4eb |
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| 2464 | 1 \chapter{The Python Debugger} |
| 2462 | 2 \stmodindex{pdb} |
| 3 \index{debugging} | |
| 4 | |
| 2464 | 5 \renewcommand{\indexsubitem}{(in module pdb)} |
| 6 | |
| 7 The module \code{pdb} defines an interactive source code debugger for | |
| 8 Python programs. It supports setting breakpoints and single stepping | |
| 9 at the source line level, inspection of stack frames, source code | |
| 10 listing, and evaluation of arbitrary Python code in the context of any | |
| 11 stack frame. It also supports post-mortem debugging and can be called | |
| 12 under program control. | |
| 2462 | 13 |
| 14 The debugger is extensible --- it is actually defined as a class | |
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15 \code{Pdb}. This is currently undocumented but easily understood by |
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16 reading the source. The extension interface uses the (also |
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17 undocumented) modules \code{bdb} and \code{cmd}. |
| 2462 | 18 \ttindex{Pdb} |
| 19 \ttindex{bdb} | |
| 20 \ttindex{cmd} | |
| 21 | |
| 22 A primitive windowing version of the debugger also exists --- this is | |
| 2464 | 23 module \code{wdb}, which requires STDWIN (see the chapter on STDWIN |
| 24 specific modules). | |
| 2462 | 25 \index{stdwin} |
| 26 \ttindex{wdb} | |
| 27 | |
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28 The debugger's prompt is ``\code{(Pdb) }''. |
| 2462 | 29 Typical usage to run a program under control of the debugger is: |
| 30 | |
| 31 \begin{verbatim} | |
| 32 >>> import pdb | |
| 33 >>> import mymodule | |
| 34 >>> pdb.run('mymodule.test()') | |
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35 > <string>(0)?() |
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36 (Pdb) continue |
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37 > <string>(1)?() |
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38 (Pdb) continue |
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39 NameError: 'spam' |
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40 > <string>(1)?() |
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41 (Pdb) |
| 2462 | 42 \end{verbatim} |
| 43 | |
| 44 Typical usage to inspect a crashed program is: | |
| 45 | |
| 46 \begin{verbatim} | |
| 47 >>> import pdb | |
| 48 >>> import mymodule | |
| 49 >>> mymodule.test() | |
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50 Traceback (innermost last): |
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51 File "<stdin>", line 1, in ? |
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52 File "./mymodule.py", line 4, in test |
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53 test2() |
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54 File "./mymodule.py", line 3, in test2 |
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55 print spam |
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56 NameError: spam |
| 2462 | 57 >>> pdb.pm() |
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58 > ./mymodule.py(3)test2() |
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59 -> print spam |
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60 (Pdb) |
| 2462 | 61 \end{verbatim} |
| 62 | |
| 63 The module defines the following functions; each enters the debugger | |
| 64 in a slightly different way: | |
| 65 | |
| 66 \begin{funcdesc}{run}{statement\optional{\, globals\optional{\, locals}}} | |
| 2464 | 67 Execute the \var{statement} (given as a string) under debugger |
| 2462 | 68 control. The debugger prompt appears before any code is executed; you |
| 2464 | 69 can set breakpoints and type \code{continue}, or you can step through |
| 70 the statement using \code{step} or \code{next} (all these commands are | |
| 71 explained below). The optional \var{globals} and \var{locals} | |
| 72 arguments specify the environment in which the code is executed; by | |
| 73 default the dictionary of the module \code{__main__} is used. (See | |
| 74 the explanation of the \code{exec} statement or the \code{eval()} | |
| 75 built-in function.) | |
| 2462 | 76 \end{funcdesc} |
| 77 | |
| 78 \begin{funcdesc}{runeval}{expression\optional{\, globals\optional{\, locals}}} | |
| 2464 | 79 Evaluate the \var{expression} (given as a a string) under debugger |
| 80 control. When \code{runeval()} returns, it returns the value of the | |
| 81 expression. Otherwise this function is similar to | |
| 2462 | 82 \code{run()}. |
| 83 \end{funcdesc} | |
| 84 | |
| 85 \begin{funcdesc}{runcall}{function\optional{\, argument\, ...}} | |
| 2464 | 86 Call the \var{function} (a function or method object, not a string) |
| 87 with the given arguments. When \code{runcall()} returns, it returns | |
| 88 whatever the function call returned. The debugger prompt appears as | |
| 89 soon as the function is entered. | |
| 2462 | 90 \end{funcdesc} |
| 91 | |
| 92 \begin{funcdesc}{set_trace}{} | |
| 93 Enter the debugger at the calling stack frame. This is useful to | |
| 2464 | 94 hard-code a breakpoint at a given point in a program, even if the code |
| 95 is not otherwise being debugged (e.g. when an assertion fails). | |
| 2462 | 96 \end{funcdesc} |
| 97 | |
| 98 \begin{funcdesc}{post_mortem}{traceback} | |
| 99 Enter post-mortem debugging of the given \var{traceback} object. | |
| 100 \end{funcdesc} | |
| 101 | |
| 102 \begin{funcdesc}{pm}{} | |
| 2464 | 103 Enter post-mortem debugging of the traceback found in |
| 2462 | 104 \code{sys.last_traceback}. |
| 105 \end{funcdesc} | |
| 106 | |
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107 \section{Debugger Commands} |
| 2462 | 108 |
| 109 The debugger recognizes the following commands. Most commands can be | |
| 110 abbreviated to one or two letters; e.g. ``\code{h(elp)}'' means that | |
| 111 either ``\code{h}'' or ``\code{help}'' can be used to enter the help | |
| 112 command (but not ``\code{he}'' or ``\code{hel}'', nor ``\code{H}'' or | |
| 113 ``\code{Help} or ``\code{HELP}''). Arguments to commands must be | |
| 114 separated by whitespace (spaces or tabs). Optional arguments are | |
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115 enclosed in square brackets (``\code{[]}'') in the command syntax; the |
| 2462 | 116 square brackets must not be typed. Alternatives in the command syntax |
| 117 are separated by a vertical bar (``\code{|}''). | |
| 118 | |
| 119 Entering a blank line repeats the last command entered. Exception: if | |
| 120 the last command was a ``\code{list}'' command, the next 11 lines are | |
| 121 listed. | |
| 122 | |
| 123 Commands that the debugger doesn't recognize are assumed to be Python | |
| 124 statements and are executed in the context of the program being | |
| 125 debugged. Python statements can also be prefixed with an exclamation | |
| 126 point (``\code{!}''). This is a powerful way to inspect the program | |
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127 being debugged; it is even possible to change a variable or call a |
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128 function. When an |
| 2462 | 129 exception occurs in such a statement, the exception name is printed |
| 130 but the debugger's state is not changed. | |
| 131 | |
| 132 \begin{description} | |
| 133 | |
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134 \item[h(elp) [\var{command}]] |
| 2462 | 135 |
| 136 Without argument, print the list of available commands. | |
| 137 With a \var{command} as argument, print help about that command. | |
| 138 ``\code{help pdb}'' displays the full documentation file; if the | |
| 139 environment variable \code{PAGER} is defined, the file is piped | |
| 2464 | 140 through that command instead. Since the \var{command} argument must be |
| 141 an identifier, ``\code{help exec}'' must be entered to get help on the | |
| 142 ``\code{!}'' command. | |
| 2462 | 143 |
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144 \item[w(here)] |
| 2462 | 145 |
| 146 Print a stack trace, with the most recent frame at the bottom. | |
| 147 An arrow indicates the current frame, which determines the | |
| 148 context of most commands. | |
| 149 | |
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150 \item[d(own)] |
| 2462 | 151 |
| 152 Move the current frame one level down in the stack trace | |
| 153 (to an older frame). | |
| 154 | |
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155 \item[u(p)] |
| 2462 | 156 |
| 157 Move the current frame one level up in the stack trace | |
| 158 (to a newer frame). | |
| 159 | |
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160 \item[b(reak) [\var{lineno}\code{|}\var{function}]] |
| 2462 | 161 |
| 162 With a \var{lineno} argument, set a break there in the current | |
| 163 file. With a \var{function} argument, set a break at the entry of | |
| 164 that function. Without argument, list all breaks. | |
| 165 | |
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166 \item[cl(ear) [\var{lineno}]] |
| 2462 | 167 |
| 168 With a \var{lineno} argument, clear that break in the current file. | |
| 169 Without argument, clear all breaks (but first ask confirmation). | |
| 170 | |
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171 \item[s(tep)] |
| 2462 | 172 |
| 173 Execute the current line, stop at the first possible occasion | |
| 174 (either in a function that is called or on the next line in the | |
| 175 current function). | |
| 176 | |
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177 \item[n(ext)] |
| 2462 | 178 |
| 179 Continue execution until the next line in the current function | |
| 180 is reached or it returns. (The difference between \code{next} and | |
| 181 \code{step} is that \code{step} stops inside a called function, while | |
| 2464 | 182 \code{next} executes called functions at (nearly) full speed, only |
| 183 stopping at the next line in the current function.) | |
| 2462 | 184 |
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185 \item[r(eturn)] |
| 2462 | 186 |
| 187 Continue execution until the current function returns. | |
| 188 | |
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189 \item[c(ont(inue))] |
| 2462 | 190 |
| 191 Continue execution, only stop when a breakpoint is encountered. | |
| 192 | |
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193 \item[l(ist) [\var{first} [, \var{last}]]] |
| 2462 | 194 |
| 2464 | 195 List source code for the current file. Without arguments, list 11 |
| 196 lines around the current line or continue the previous listing. With | |
| 197 one argument, list 11 lines around at that line. With two arguments, | |
| 198 list the given range; if the second argument is less than the first, | |
| 199 it is interpreted as a count. | |
| 2462 | 200 |
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201 \item[a(rgs)] |
| 2462 | 202 |
| 203 Print the argument list of the current function. | |
| 204 | |
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205 \item[p \var{expression}] |
| 2462 | 206 |
| 207 Evaluate the \var{expression} in the current context and print its | |
| 2464 | 208 value. (Note: \code{print} can also be used, but is not a debugger |
| 209 command --- this executes the Python \code{print} statement.) | |
| 2462 | 210 |
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211 \item[[!] \var{statement}] |
| 2462 | 212 |
| 213 Execute the (one-line) \var{statement} in the context of | |
| 214 the current stack frame. | |
| 215 The exclamation point can be omitted unless the first word | |
| 216 of the statement resembles a debugger command. | |
| 217 To set a global variable, you can prefix the assignment | |
| 218 command with a ``\code{global}'' command on the same line, e.g.: | |
| 219 \begin{verbatim} | |
| 220 (Pdb) global list_options; list_options = ['-l'] | |
| 221 (Pdb) | |
| 222 \end{verbatim} | |
| 223 | |
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224 \item[q(uit)] |
| 2462 | 225 |
| 226 Quit from the debugger. | |
| 227 The program being executed is aborted. | |
| 228 | |
| 229 \end{description} | |
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230 |
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231 \section{How It Works} |
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232 |
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233 Some changes were made to the interpreter: |
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234 |
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235 \begin{itemize} |
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236 \item sys.settrace(func) sets the global trace function |
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237 \item there can also a local trace function (see later) |
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238 \end{itemize} |
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239 |
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240 Trace functions have three arguments: (\var{frame}, \var{event}, \var{arg}) |
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241 |
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242 \begin{description} |
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243 |
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244 \item[\var{frame}] is the current stack frame |
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245 |
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246 \item[\var{event}] is a string: \code{'call'}, \code{'line'}, \code{'return'} |
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247 or \code{'exception'} |
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248 |
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249 \item[\var{arg}] is dependent on the event type |
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250 |
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251 \end{description} |
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252 |
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253 A trace function should return a new trace function or None. |
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254 Class methods are accepted (and most useful!) as trace methods. |
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255 |
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256 The events have the following meaning: |
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257 |
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258 \begin{description} |
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259 |
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260 \item[\code{'call'}] |
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261 A function is called (or some other code block entered). The global |
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262 trace function is called; arg is the argument list to the function; |
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263 the return value specifies the local trace function. |
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264 |
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265 \item[\code{'line'}] |
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266 The interpreter is about to execute a new line of code (sometimes |
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267 multiple line events on one line exist). The local trace function is |
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268 called; arg in None; the return value specifies the new local trace |
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269 function. |
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270 |
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271 \item[\code{'return'}] |
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272 A function (or other code block) is about to return. The local trace |
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273 function is called; arg is the value that will be returned. The trace |
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274 function's return value is ignored. |
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275 |
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276 \item[\code{'exception'}] |
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277 An exception has occurred. The local trace function is called; arg is |
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278 a triple (exception, value, traceback); the return value specifies the |
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279 new local trace function |
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280 |
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281 \end{description} |
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282 |
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283 Note that as an exception is propagated down the chain of callers, an |
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284 \code{'exception'} event is generated at each level. |
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285 |
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286 Stack frame objects have the following read-only attributes: |
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287 |
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288 \begin{description} |
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289 \item[f_code] the code object being executed |
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290 \item[f_lineno] the current line number (\code{-1} for \code{'call'} events) |
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291 \item[f_back] the stack frame of the caller, or None |
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292 \item[f_locals] dictionary containing local name bindings |
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293 \item[f_globals] dictionary containing global name bindings |
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294 \end{description} |
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295 |
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296 Code objects have the following read-only attributes: |
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297 |
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298 \begin{description} |
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299 \item[co_code] the code string |
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300 \item[co_names] the list of names used by the code |
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301 \item[co_consts] the list of (literal) constants used by the code |
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302 \item[co_filename] the filename from which the code was compiled |
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303 \end{description} |