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