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/Doc/library/bdb.rst

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  1:mod:`bdb` --- Debugger framework
  2=================================
  3
  4.. module:: bdb
  5   :synopsis: Debugger framework.
  6
  7The :mod:`bdb` module handles basic debugger functions, like setting breakpoints
  8or managing execution via the debugger.
  9
 10The following exception is defined:
 11
 12.. exception:: BdbQuit
 13
 14   Exception raised by the :class:`Bdb` class for quitting the debugger.
 15
 16
 17The :mod:`bdb` module also defines two classes:
 18
 19.. class:: Breakpoint(self, file, line[, temporary=0[, cond=None [, funcname=None]]])
 20
 21   This class implements temporary breakpoints, ignore counts, disabling and
 22   (re-)enabling, and conditionals.
 23
 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.
 28
 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
 32   counts a hit.
 33
 34   :class:`Breakpoint` instances have the following methods:
 35
 36   .. method:: deleteMe()
 37
 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
 40      file/line.
 41
 42
 43   .. method:: enable()
 44
 45      Mark the breakpoint as enabled.
 46
 47
 48   .. method:: disable()
 49
 50      Mark the breakpoint as disabled.
 51
 52
 53   .. method:: pprint([out])
 54
 55      Print all the information about the breakpoint:
 56
 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.
 63
 64
 65.. class:: Bdb()
 66
 67   The :class:`Bdb` acts as a generic Python debugger base class.
 68
 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.
 72
 73
 74   The following methods of :class:`Bdb` normally don't need to be overridden.
 75
 76   .. method:: canonic(filename)
 77
 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.
 81
 82   .. method:: reset()
 83
 84      Set the :attr:`botframe`, :attr:`stopframe`, :attr:`returnframe` and
 85      :attr:`quitting` attributes with values ready to start debugging.
 86
 87   .. method:: trace_dispatch(frame, event, arg)
 88
 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).
 91
 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:
 95
 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
 98        entered.
 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.
104
105      For the Python events, specialized functions (see below) are called.  For
106      the C events, no action is taken.
107
108      The *arg* parameter depends on the previous event.
109
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
112      :ref:`types`.
113
114   .. method:: dispatch_line(frame)
115
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.
121
122   .. method:: dispatch_call(frame, arg)
123
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.
129
130   .. method:: dispatch_return(frame, arg)
131
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.
137
138   .. method:: dispatch_exception(frame, arg)
139
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.
145
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.
148
149   .. method:: stop_here(frame)
150
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.
153
154   .. method:: break_here(frame)
155
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.
159
160   .. method:: break_anywhere(frame)
161
162      This method checks if there is a breakpoint in the filename of the current
163      frame.
164
165   Derived classes should override these methods to gain control over debugger
166   operation.
167
168   .. method:: user_call(frame, argument_list)
169
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
172      function.
173
174   .. method:: user_line(frame)
175
176      This method is called from :meth:`dispatch_line` when either
177      :meth:`stop_here` or :meth:`break_here` yields True.
178
179   .. method:: user_return(frame, return_value)
180
181      This method is called from :meth:`dispatch_return` when :meth:`stop_here`
182      yields True.
183
184   .. method:: user_exception(frame, exc_info)
185
186      This method is called from :meth:`dispatch_exception` when
187      :meth:`stop_here` yields True.
188
189   .. method:: do_clear(arg)
190
191      Handle how a breakpoint must be removed when it is a temporary one.
192
193      This method must be implemented by derived classes.
194
195
196   Derived classes and clients can call the following methods to affect the
197   stepping state.
198
199   .. method:: set_step()
200
201      Stop after one line of code.
202
203   .. method:: set_next(frame)
204
205      Stop on the next line in or below the given frame.
206
207   .. method:: set_return(frame)
208
209      Stop when returning from the given frame.
210
211   .. method:: set_until(frame)
212
213      Stop when the line with the line no greater than the current one is
214      reached or when returning from current frame
215
216   .. method:: set_trace([frame])
217
218      Start debugging from *frame*.  If *frame* is not specified, debugging
219      starts from caller's frame.
220
221   .. method:: set_continue()
222
223      Stop only at breakpoints or when finished.  If there are no breakpoints,
224      set the system trace function to None.
225
226   .. method:: set_quit()
227
228      Set the :attr:`quitting` attribute to True.  This raises :exc:`BdbQuit` in
229      the next call to one of the :meth:`dispatch_\*` methods.
230
231
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.
235
236   .. method:: set_break(filename, lineno[, temporary=0[, cond[, funcname]]])
237
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.
241
242   .. method:: clear_break(filename, lineno)
243
244      Delete the breakpoints in *filename* and *lineno*.  If none were set, an
245      error message is returned.
246
247   .. method:: clear_bpbynumber(arg)
248
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.
252
253   .. method:: clear_all_file_breaks(filename)
254
255      Delete all breakpoints in *filename*.  If none were set, an error message
256      is returned.
257
258   .. method:: clear_all_breaks()
259
260      Delete all existing breakpoints.
261
262   .. method:: get_break(filename, lineno)
263
264      Check if there is a breakpoint for *lineno* of *filename*.
265
266   .. method:: get_breaks(filename, lineno)
267
268      Return all breakpoints for *lineno* in *filename*, or an empty list if
269      none are set.
270
271   .. method:: get_file_breaks(filename)
272
273      Return all breakpoints in *filename*, or an empty list if none are set.
274
275   .. method:: get_all_breaks()
276
277      Return all breakpoints that are set.
278
279
280   Derived classes and clients can call the following methods to get a data
281   structure representing a stack trace.
282
283   .. method:: get_stack(f, t)
284
285      Get a list of records for a frame and all higher (calling) and lower
286      frames, and the size of the higher part.
287
288   .. method:: format_stack_entry(frame_lineno, [lprefix=': '])
289
290      Return a string with information about a stack entry, identified by a
291      ``(frame, lineno)`` tuple:
292
293      * The canonical form of the filename which contains the frame.
294      * The function name, or ``"<lambda>"``.
295      * The input arguments.
296      * The return value.
297      * The line of code (if it exists).
298
299
300   The following two methods can be called by clients to use a debugger to debug
301   a :term:`statement`, given as a string.
302
303   .. method:: run(cmd, [globals, [locals]])
304
305      Debug a statement executed via the :keyword:`exec` statement.  *globals*
306      defaults to :attr:`__main__.__dict__`, *locals* defaults to *globals*.
307
308   .. method:: runeval(expr, [globals, [locals]])
309
310      Debug an expression executed via the :func:`eval` function.  *globals* and
311      *locals* have the same meaning as in :meth:`run`.
312
313   .. method:: runctx(cmd, globals, locals)
314
315      For backwards compatibility.  Calls the :meth:`run` method.
316
317   .. method:: runcall(func, *args, **kwds)
318
319      Debug a single function call, and return its result.
320
321
322Finally, the module defines the following functions:
323
324.. function:: checkfuncname(b, frame)
325
326   Check whether we should break here, depending on the way the breakpoint *b*
327   was set.
328
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.
333
334.. function:: effective(file, line, frame)
335
336   Determine if there is an effective (active) breakpoint at this line of code.
337   Return breakpoint number or 0 if none.
338
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.
342
343.. function:: set_trace()
344
345   Starts debugging with a :class:`Bdb` instance from caller's frame.