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 For more information on trace functions, see :ref:`debugger-hooks`. For
111 more information on code and frame objects, refer to :ref:`types`.
113 .. method:: dispatch_line(frame)
115 If the debugger should stop on the current line, invoke the
116 :meth:`user_line` method (which should be overridden in subclasses).
117 Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
118 (which can be set from :meth:`user_line`). Return a reference to the
119 :meth:`trace_dispatch` method for further tracing in that scope.
121 .. method:: dispatch_call(frame, arg)
123 If the debugger should stop on this function call, invoke the
124 :meth:`user_call` method (which should be overridden in subclasses).
125 Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
126 (which can be set from :meth:`user_call`). Return a reference to the
127 :meth:`trace_dispatch` method for further tracing in that scope.
129 .. method:: dispatch_return(frame, arg)
131 If the debugger should stop on this function return, invoke the
132 :meth:`user_return` method (which should be overridden in subclasses).
133 Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
134 (which can be set from :meth:`user_return`). Return a reference to the
135 :meth:`trace_dispatch` method for further tracing in that scope.
137 .. method:: dispatch_exception(frame, arg)
139 If the debugger should stop at this exception, invokes the
140 :meth:`user_exception` method (which should be overridden in subclasses).
141 Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
142 (which can be set from :meth:`user_exception`). Return a reference to the
143 :meth:`trace_dispatch` method for further tracing in that scope.
145 Normally derived classes don't override the following methods, but they may
146 if they want to redefine the definition of stopping and breakpoints.
148 .. method:: stop_here(frame)
150 This method checks if the *frame* is somewhere below :attr:`botframe` in
151 the call stack. :attr:`botframe` is the frame in which debugging started.
153 .. method:: break_here(frame)
155 This method checks if there is a breakpoint in the filename and line
156 belonging to *frame* or, at least, in the current function. If the
157 breakpoint is a temporary one, this method deletes it.
159 .. method:: break_anywhere(frame)
161 This method checks if there is a breakpoint in the filename of the current
164 Derived classes should override these methods to gain control over debugger
167 .. method:: user_call(frame, argument_list)
169 This method is called from :meth:`dispatch_call` when there is the
170 possibility that a break might be necessary anywhere inside the called
173 .. method:: user_line(frame)
175 This method is called from :meth:`dispatch_line` when either
176 :meth:`stop_here` or :meth:`break_here` yields True.
178 .. method:: user_return(frame, return_value)
180 This method is called from :meth:`dispatch_return` when :meth:`stop_here`
183 .. method:: user_exception(frame, exc_info)
185 This method is called from :meth:`dispatch_exception` when
186 :meth:`stop_here` yields True.
188 .. method:: do_clear(arg)
190 Handle how a breakpoint must be removed when it is a temporary one.
192 This method must be implemented by derived classes.
195 Derived classes and clients can call the following methods to affect the
198 .. method:: set_step()
200 Stop after one line of code.
202 .. method:: set_next(frame)
204 Stop on the next line in or below the given frame.
206 .. method:: set_return(frame)
208 Stop when returning from the given frame.
210 .. method:: set_until(frame)
212 Stop when the line with the line no greater than the current one is
213 reached or when returning from current frame
215 .. method:: set_trace([frame])
217 Start debugging from *frame*. If *frame* is not specified, debugging
218 starts from caller's frame.
220 .. method:: set_continue()
222 Stop only at breakpoints or when finished. If there are no breakpoints,
223 set the system trace function to None.
225 .. method:: set_quit()
227 Set the :attr:`quitting` attribute to True. This raises :exc:`BdbQuit` in
228 the next call to one of the :meth:`dispatch_\*` methods.
231 Derived classes and clients can call the following methods to manipulate
232 breakpoints. These methods return a string containing an error message if
233 something went wrong, or ``None`` if all is well.
235 .. method:: set_break(filename, lineno[, temporary=0[, cond[, funcname]]])
237 Set a new breakpoint. If the *lineno* line doesn't exist for the
238 *filename* passed as argument, return an error message. The *filename*
239 should be in canonical form, as described in the :meth:`canonic` method.
241 .. method:: clear_break(filename, lineno)
243 Delete the breakpoints in *filename* and *lineno*. If none were set, an
244 error message is returned.
246 .. method:: clear_bpbynumber(arg)
248 Delete the breakpoint which has the index *arg* in the
249 :attr:`Breakpoint.bpbynumber`. If *arg* is not numeric or out of range,
250 return an error message.
252 .. method:: clear_all_file_breaks(filename)
254 Delete all breakpoints in *filename*. If none were set, an error message
257 .. method:: clear_all_breaks()
259 Delete all existing breakpoints.
261 .. method:: get_break(filename, lineno)
263 Check if there is a breakpoint for *lineno* of *filename*.
265 .. method:: get_breaks(filename, lineno)
267 Return all breakpoints for *lineno* in *filename*, or an empty list if
270 .. method:: get_file_breaks(filename)
272 Return all breakpoints in *filename*, or an empty list if none are set.
274 .. method:: get_all_breaks()
276 Return all breakpoints that are set.
279 Derived classes and clients can call the following methods to get a data
280 structure representing a stack trace.
282 .. method:: get_stack(f, t)
284 Get a list of records for a frame and all higher (calling) and lower
285 frames, and the size of the higher part.
287 .. method:: format_stack_entry(frame_lineno, [lprefix=': '])
289 Return a string with information about a stack entry, identified by a
290 ``(frame, lineno)`` tuple:
292 * The canonical form of the filename which contains the frame.
293 * The function name, or ``"<lambda>"``.
294 * The input arguments.
296 * The line of code (if it exists).
299 The following two methods can be called by clients to use a debugger to debug
300 a :term:`statement`, given as a string.
302 .. method:: run(cmd, [globals, [locals]])
304 Debug a statement executed via the :keyword:`exec` statement. *globals*
305 defaults to :attr:`__main__.__dict__`, *locals* defaults to *globals*.
307 .. method:: runeval(expr, [globals, [locals]])
309 Debug an expression executed via the :func:`eval` function. *globals* and
310 *locals* have the same meaning as in :meth:`run`.
312 .. method:: runctx(cmd, globals, locals)
314 For backwards compatibility. Calls the :meth:`run` method.
316 .. method:: runcall(func, *args, **kwds)
318 Debug a single function call, and return its result.
321 Finally, the module defines the following functions:
323 .. function:: checkfuncname(b, frame)
325 Check whether we should break here, depending on the way the breakpoint *b*
328 If it was set via line number, it checks if ``b.line`` is the same as the one
329 in the frame also passed as argument. If the breakpoint was set via function
330 name, we have to check we are in the right frame (the right function) and if
331 we are in its first executable line.
333 .. function:: effective(file, line, frame)
335 Determine if there is an effective (active) breakpoint at this line of code.
336 Return breakpoint number or 0 if none.
338 Called only if we know there is a breakpoint at this location. Returns the
339 breakpoint that was triggered and a flag that indicates if it is ok to delete
340 a temporary breakpoint.
342 .. function:: set_trace()
344 Starts debugging with a :class:`Bdb` instance from caller's frame.