/Doc/library/bdb.rst
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- :mod:`bdb` --- Debugger framework
- =================================
- .. module:: bdb
- :synopsis: Debugger framework.
- The :mod:`bdb` module handles basic debugger functions, like setting breakpoints
- or managing execution via the debugger.
- The following exception is defined:
- .. exception:: BdbQuit
- Exception raised by the :class:`Bdb` class for quitting the debugger.
- The :mod:`bdb` module also defines two classes:
- .. class:: Breakpoint(self, file, line[, temporary=0[, cond=None [, funcname=None]]])
- This class implements temporary breakpoints, ignore counts, disabling and
- (re-)enabling, and conditionals.
- Breakpoints are indexed by number through a list called :attr:`bpbynumber`
- and by ``(file, line)`` pairs through :attr:`bplist`. The former points to a
- single instance of class :class:`Breakpoint`. The latter points to a list of
- such instances since there may be more than one breakpoint per line.
- When creating a breakpoint, its associated filename should be in canonical
- form. If a *funcname* is defined, a breakpoint hit will be counted when the
- first line of that function is executed. A conditional breakpoint always
- counts a hit.
- :class:`Breakpoint` instances have the following methods:
- .. method:: deleteMe()
- Delete the breakpoint from the list associated to a file/line. If it is
- the last breakpoint in that position, it also deletes the entry for the
- file/line.
- .. method:: enable()
- Mark the breakpoint as enabled.
- .. method:: disable()
- Mark the breakpoint as disabled.
- .. method:: pprint([out])
- Print all the information about the breakpoint:
- * The breakpoint number.
- * If it is temporary or not.
- * Its file,line position.
- * The condition that causes a break.
- * If it must be ignored the next N times.
- * The breakpoint hit count.
- .. class:: Bdb()
- The :class:`Bdb` acts as a generic Python debugger base class.
- This class takes care of the details of the trace facility; a derived class
- should implement user interaction. The standard debugger class
- (:class:`pdb.Pdb`) is an example.
- The following methods of :class:`Bdb` normally don't need to be overridden.
- .. method:: canonic(filename)
- Auxiliary method for getting a filename in a canonical form, that is, as a
- case-normalized (on case-insensitive filesystems) absolute path, stripped
- of surrounding angle brackets.
- .. method:: reset()
- Set the :attr:`botframe`, :attr:`stopframe`, :attr:`returnframe` and
- :attr:`quitting` attributes with values ready to start debugging.
- .. method:: trace_dispatch(frame, event, arg)
- This function is installed as the trace function of debugged frames. Its
- return value is the new trace function (in most cases, that is, itself).
- The default implementation decides how to dispatch a frame, depending on
- the type of event (passed as a string) that is about to be executed.
- *event* can be one of the following:
- * ``"line"``: A new line of code is going to be executed.
- * ``"call"``: A function is about to be called, or another code block
- entered.
- * ``"return"``: A function or other code block is about to return.
- * ``"exception"``: An exception has occurred.
- * ``"c_call"``: A C function is about to be called.
- * ``"c_return"``: A C function has returned.
- * ``"c_exception"``: A C function has thrown an exception.
- For the Python events, specialized functions (see below) are called. For
- the C events, no action is taken.
- The *arg* parameter depends on the previous event.
- See the documentation for :func:`sys.settrace` for more information on the
- trace function. For more information on code and frame objects, refer to
- :ref:`types`.
- .. method:: dispatch_line(frame)
- If the debugger should stop on the current line, invoke the
- :meth:`user_line` method (which should be overridden in subclasses).
- Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
- (which can be set from :meth:`user_line`). Return a reference to the
- :meth:`trace_dispatch` method for further tracing in that scope.
- .. method:: dispatch_call(frame, arg)
- If the debugger should stop on this function call, invoke the
- :meth:`user_call` method (which should be overridden in subclasses).
- Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
- (which can be set from :meth:`user_call`). Return a reference to the
- :meth:`trace_dispatch` method for further tracing in that scope.
- .. method:: dispatch_return(frame, arg)
- If the debugger should stop on this function return, invoke the
- :meth:`user_return` method (which should be overridden in subclasses).
- Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
- (which can be set from :meth:`user_return`). Return a reference to the
- :meth:`trace_dispatch` method for further tracing in that scope.
- .. method:: dispatch_exception(frame, arg)
- If the debugger should stop at this exception, invokes the
- :meth:`user_exception` method (which should be overridden in subclasses).
- Raise a :exc:`BdbQuit` exception if the :attr:`Bdb.quitting` flag is set
- (which can be set from :meth:`user_exception`). Return a reference to the
- :meth:`trace_dispatch` method for further tracing in that scope.
- Normally derived classes don't override the following methods, but they may
- if they want to redefine the definition of stopping and breakpoints.
- .. method:: stop_here(frame)
- This method checks if the *frame* is somewhere below :attr:`botframe` in
- the call stack. :attr:`botframe` is the frame in which debugging started.
- .. method:: break_here(frame)
- This method checks if there is a breakpoint in the filename and line
- belonging to *frame* or, at least, in the current function. If the
- breakpoint is a temporary one, this method deletes it.
- .. method:: break_anywhere(frame)
- This method checks if there is a breakpoint in the filename of the current
- frame.
- Derived classes should override these methods to gain control over debugger
- operation.
- .. method:: user_call(frame, argument_list)
- This method is called from :meth:`dispatch_call` when there is the
- possibility that a break might be necessary anywhere inside the called
- function.
- .. method:: user_line(frame)
- This method is called from :meth:`dispatch_line` when either
- :meth:`stop_here` or :meth:`break_here` yields True.
- .. method:: user_return(frame, return_value)
- This method is called from :meth:`dispatch_return` when :meth:`stop_here`
- yields True.
- .. method:: user_exception(frame, exc_info)
- This method is called from :meth:`dispatch_exception` when
- :meth:`stop_here` yields True.
- .. method:: do_clear(arg)
- Handle how a breakpoint must be removed when it is a temporary one.
- This method must be implemented by derived classes.
- Derived classes and clients can call the following methods to affect the
- stepping state.
- .. method:: set_step()
- Stop after one line of code.
- .. method:: set_next(frame)
- Stop on the next line in or below the given frame.
- .. method:: set_return(frame)
- Stop when returning from the given frame.
- .. method:: set_until(frame)
- Stop when the line with the line no greater than the current one is
- reached or when returning from current frame
- .. method:: set_trace([frame])
- Start debugging from *frame*. If *frame* is not specified, debugging
- starts from caller's frame.
- .. method:: set_continue()
- Stop only at breakpoints or when finished. If there are no breakpoints,
- set the system trace function to None.
- .. method:: set_quit()
- Set the :attr:`quitting` attribute to True. This raises :exc:`BdbQuit` in
- the next call to one of the :meth:`dispatch_\*` methods.
- Derived classes and clients can call the following methods to manipulate
- breakpoints. These methods return a string containing an error message if
- something went wrong, or ``None`` if all is well.
- .. method:: set_break(filename, lineno[, temporary=0[, cond[, funcname]]])
- Set a new breakpoint. If the *lineno* line doesn't exist for the
- *filename* passed as argument, return an error message. The *filename*
- should be in canonical form, as described in the :meth:`canonic` method.
- .. method:: clear_break(filename, lineno)
- Delete the breakpoints in *filename* and *lineno*. If none were set, an
- error message is returned.
- .. method:: clear_bpbynumber(arg)
- Delete the breakpoint which has the index *arg* in the
- :attr:`Breakpoint.bpbynumber`. If *arg* is not numeric or out of range,
- return an error message.
- .. method:: clear_all_file_breaks(filename)
- Delete all breakpoints in *filename*. If none were set, an error message
- is returned.
- .. method:: clear_all_breaks()
- Delete all existing breakpoints.
- .. method:: get_break(filename, lineno)
- Check if there is a breakpoint for *lineno* of *filename*.
- .. method:: get_breaks(filename, lineno)
- Return all breakpoints for *lineno* in *filename*, or an empty list if
- none are set.
- .. method:: get_file_breaks(filename)
- Return all breakpoints in *filename*, or an empty list if none are set.
- .. method:: get_all_breaks()
- Return all breakpoints that are set.
- Derived classes and clients can call the following methods to get a data
- structure representing a stack trace.
- .. method:: get_stack(f, t)
- Get a list of records for a frame and all higher (calling) and lower
- frames, and the size of the higher part.
- .. method:: format_stack_entry(frame_lineno, [lprefix=': '])
- Return a string with information about a stack entry, identified by a
- ``(frame, lineno)`` tuple:
- * The canonical form of the filename which contains the frame.
- * The function name, or ``"<lambda>"``.
- * The input arguments.
- * The return value.
- * The line of code (if it exists).
- The following two methods can be called by clients to use a debugger to debug
- a :term:`statement`, given as a string.
- .. method:: run(cmd, [globals, [locals]])
- Debug a statement executed via the :keyword:`exec` statement. *globals*
- defaults to :attr:`__main__.__dict__`, *locals* defaults to *globals*.
- .. method:: runeval(expr, [globals, [locals]])
- Debug an expression executed via the :func:`eval` function. *globals* and
- *locals* have the same meaning as in :meth:`run`.
- .. method:: runctx(cmd, globals, locals)
- For backwards compatibility. Calls the :meth:`run` method.
- .. method:: runcall(func, *args, **kwds)
- Debug a single function call, and return its result.
- Finally, the module defines the following functions:
- .. function:: checkfuncname(b, frame)
- Check whether we should break here, depending on the way the breakpoint *b*
- was set.
- If it was set via line number, it checks if ``b.line`` is the same as the one
- in the frame also passed as argument. If the breakpoint was set via function
- name, we have to check we are in the right frame (the right function) and if
- we are in its first executable line.
- .. function:: effective(file, line, frame)
- Determine if there is an effective (active) breakpoint at this line of code.
- Return breakpoint number or 0 if none.
- Called only if we know there is a breakpoint at this location. Returns the
- breakpoint that was triggered and a flag that indicates if it is ok to delete
- a temporary breakpoint.
- .. function:: set_trace()
- Starts debugging with a :class:`Bdb` instance from caller's frame.