1 :mod:`bdb` --- Debugger framework
2 =================================
5 :synopsis: Debugger framework.
7 The :mod:`bdb` module handles basic debugger functions, like setting breakpoints
8 or managing execution via the debugger.
10 The following exception is defined:
12 .. exception:: BdbQuit
14 Exception raised by the :class:`Bdb` class for quitting the debugger.
17 The :mod:`bdb` module also defines two classes:
19 .. class:: Breakpoint(self, file, line[, temporary=0[, cond=None [, funcname=None]]])
21 This class implements temporary breakpoints, ignore counts, disabling and
22 (re-)enabling, and conditionals.
24 Breakpoints are indexed by number through a list called :attr:`bpbynumber`
25 and by ``(file, line)`` pairs through :attr:`bplist`. The former points to a
26 single instance of class :class:`Breakpoint`. The latter points to a list of
27 such instances since there may be more than one breakpoint per line.
29 When creating a breakpoint, its associated filename should be in canonical
30 form. If a *funcname* is defined, a breakpoint hit will be counted when the
31 first line of that function is executed. A conditional breakpoint always
34 :class:`Breakpoint` instances have the following methods:
36 .. method:: deleteMe()
38 Delete the breakpoint from the list associated to a file/line. If it is
39 the last breakpoint in that position, it also deletes the entry for the
45 Mark the breakpoint as enabled.
50 Mark the breakpoint as disabled.
53 .. method:: pprint([out])
55 Print all the information about the breakpoint:
57 * The breakpoint number.
58 * If it is temporary or not.
59 * Its file,line position.
60 * The condition that causes a break.
61 * If it must be ignored the next N times.
62 * The breakpoint hit count.
67 The :class:`Bdb` acts as a generic Python debugger base class.
69 This class takes care of the details of the trace facility; a derived class
70 should implement user interaction. The standard debugger class
71 (:class:`pdb.Pdb`) is an example.
74 The following methods of :class:`Bdb` normally don't need to be overridden.
76 .. method:: canonic(filename)
78 Auxiliary method for getting a filename in a canonical form, that is, as a
79 case-normalized (on case-insensitive filesystems) absolute path, stripped
80 of surrounding angle brackets.
84 Set the :attr:`botframe`, :attr:`stopframe`, :attr:`returnframe` and
85 :attr:`quitting` attributes with values ready to start debugging.
87 .. method:: trace_dispatch(frame, event, arg)
89 This function is installed as the trace function of debugged frames. Its
90 return value is the new trace function (in most cases, that is, itself).
92 The default implementation decides how to dispatch a frame, depending on
93 the type of event (passed as a string) that is about to be executed.
94 *event* can be one of the following:
96 * ``"line"``: A new line of code is going to be executed.
97 * ``"call"``: A function is about to be called, or another code block
99 * ``"return"``: A function or other code block is about to return.
100 * ``"exception"``: An exception has occurred.
101 * ``"c_call"``: A C function is about to be called.
102 * ``"c_return"``: A C function has returned.
103 * ``"c_exception"``: A C function has thrown an exception.
105 For the Python events, specialized functions (see below) are called. For
106 the C events, no action is taken.
108 The *arg* parameter depends on the previous event.
110 See the documentation for :func:`sys.settrace` for more information on the
111 trace function. For more information on code and frame objects, refer to
114 .. method:: dispatch_line(frame)
116 If the debugger should stop on the current line, invoke the
117 :meth:`user_line` method (which should be overridden in subclasses).
118 Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
119 (which can be set from :meth:`user_line`). Return a reference to the
120 :meth:`trace_dispatch` method for further tracing in that scope.
122 .. method:: dispatch_call(frame, arg)
124 If the debugger should stop on this function call, invoke the
125 :meth:`user_call` method (which should be overridden in subclasses).
126 Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
127 (which can be set from :meth:`user_call`). Return a reference to the
128 :meth:`trace_dispatch` method for further tracing in that scope.
130 .. method:: dispatch_return(frame, arg)
132 If the debugger should stop on this function return, invoke the
133 :meth:`user_return` method (which should be overridden in subclasses).
134 Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
135 (which can be set from :meth:`user_return`). Return a reference to the
136 :meth:`trace_dispatch` method for further tracing in that scope.
138 .. method:: dispatch_exception(frame, arg)
140 If the debugger should stop at this exception, invokes the
141 :meth:`user_exception` method (which should be overridden in subclasses).
142 Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
143 (which can be set from :meth:`user_exception`). Return a reference to the
144 :meth:`trace_dispatch` method for further tracing in that scope.
146 Normally derived classes don't override the following methods, but they may
147 if they want to redefine the definition of stopping and breakpoints.
149 .. method:: stop_here(frame)
151 This method checks if the *frame* is somewhere below :attr:`botframe` in
152 the call stack. :attr:`botframe` is the frame in which debugging started.
154 .. method:: break_here(frame)
156 This method checks if there is a breakpoint in the filename and line
157 belonging to *frame* or, at least, in the current function. If the
158 breakpoint is a temporary one, this method deletes it.
160 .. method:: break_anywhere(frame)
162 This method checks if there is a breakpoint in the filename of the current
165 Derived classes should override these methods to gain control over debugger
168 .. method:: user_call(frame, argument_list)
170 This method is called from :meth:`dispatch_call` when there is the
171 possibility that a break might be necessary anywhere inside the called
174 .. method:: user_line(frame)
176 This method is called from :meth:`dispatch_line` when either
177 :meth:`stop_here` or :meth:`break_here` yields True.
179 .. method:: user_return(frame, return_value)
181 This method is called from :meth:`dispatch_return` when :meth:`stop_here`
184 .. method:: user_exception(frame, exc_info)
186 This method is called from :meth:`dispatch_exception` when
187 :meth:`stop_here` yields True.
189 .. method:: do_clear(arg)
191 Handle how a breakpoint must be removed when it is a temporary one.
193 This method must be implemented by derived classes.
196 Derived classes and clients can call the following methods to affect the
199 .. method:: set_step()
201 Stop after one line of code.
203 .. method:: set_next(frame)
205 Stop on the next line in or below the given frame.
207 .. method:: set_return(frame)
209 Stop when returning from the given frame.
211 .. method:: set_until(frame)
213 Stop when the line with the line no greater than the current one is
214 reached or when returning from current frame
216 .. method:: set_trace([frame])
218 Start debugging from *frame*. If *frame* is not specified, debugging
219 starts from caller's frame.
221 .. method:: set_continue()
223 Stop only at breakpoints or when finished. If there are no breakpoints,
224 set the system trace function to None.
226 .. method:: set_quit()
228 Set the :attr:`quitting` attribute to True. This raises :exc:`BdbQuit` in
229 the next call to one of the :meth:`dispatch_\*` methods.
232 Derived classes and clients can call the following methods to manipulate
233 breakpoints. These methods return a string containing an error message if
234 something went wrong, or ``None`` if all is well.
236 .. method:: set_break(filename, lineno[, temporary=0[, cond[, funcname]]])
238 Set a new breakpoint. If the *lineno* line doesn't exist for the
239 *filename* passed as argument, return an error message. The *filename*
240 should be in canonical form, as described in the :meth:`canonic` method.
242 .. method:: clear_break(filename, lineno)
244 Delete the breakpoints in *filename* and *lineno*. If none were set, an
245 error message is returned.
247 .. method:: clear_bpbynumber(arg)
249 Delete the breakpoint which has the index *arg* in the
250 :attr:`Breakpoint.bpbynumber`. If *arg* is not numeric or out of range,
251 return an error message.
253 .. method:: clear_all_file_breaks(filename)
255 Delete all breakpoints in *filename*. If none were set, an error message
258 .. method:: clear_all_breaks()
260 Delete all existing breakpoints.
262 .. method:: get_break(filename, lineno)
264 Check if there is a breakpoint for *lineno* of *filename*.
266 .. method:: get_breaks(filename, lineno)
268 Return all breakpoints for *lineno* in *filename*, or an empty list if
271 .. method:: get_file_breaks(filename)
273 Return all breakpoints in *filename*, or an empty list if none are set.
275 .. method:: get_all_breaks()
277 Return all breakpoints that are set.
280 Derived classes and clients can call the following methods to get a data
281 structure representing a stack trace.
283 .. method:: get_stack(f, t)
285 Get a list of records for a frame and all higher (calling) and lower
286 frames, and the size of the higher part.
288 .. method:: format_stack_entry(frame_lineno, [lprefix=': '])
290 Return a string with information about a stack entry, identified by a
291 ``(frame, lineno)`` tuple:
293 * The canonical form of the filename which contains the frame.
294 * The function name, or ``"<lambda>"``.
295 * The input arguments.
297 * The line of code (if it exists).
300 The following two methods can be called by clients to use a debugger to debug
301 a :term:`statement`, given as a string.
303 .. method:: run(cmd, [globals, [locals]])
305 Debug a statement executed via the :keyword:`exec` statement. *globals*
306 defaults to :attr:`__main__.__dict__`, *locals* defaults to *globals*.
308 .. method:: runeval(expr, [globals, [locals]])
310 Debug an expression executed via the :func:`eval` function. *globals* and
311 *locals* have the same meaning as in :meth:`run`.
313 .. method:: runctx(cmd, globals, locals)
315 For backwards compatibility. Calls the :meth:`run` method.
317 .. method:: runcall(func, *args, **kwds)
319 Debug a single function call, and return its result.
322 Finally, the module defines the following functions:
324 .. function:: checkfuncname(b, frame)
326 Check whether we should break here, depending on the way the breakpoint *b*
329 If it was set via line number, it checks if ``b.line`` is the same as the one
330 in the frame also passed as argument. If the breakpoint was set via function
331 name, we have to check we are in the right frame (the right function) and if
332 we are in its first executable line.
334 .. function:: effective(file, line, frame)
336 Determine if there is an effective (active) breakpoint at this line of code.
337 Return breakpoint number or 0 if none.
339 Called only if we know there is a breakpoint at this location. Returns the
340 breakpoint that was triggered and a flag that indicates if it is ok to delete
341 a temporary breakpoint.
343 .. function:: set_trace()
345 Starts debugging with a :class:`Bdb` instance from caller's frame.