: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.

      For more information on trace functions, see :ref:`debugger-hooks`.  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.