"bdb" — Debugger framework
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**Source code:** Lib/bdb.py

======================================================================

The "bdb" module handles basic debugger functions, like setting
breakpoints or managing execution via the debugger.

The following exception is defined:

exception bdb.BdbQuit

   Exception raised by the "Bdb" class for quitting the debugger.

The "bdb" module also defines two classes:

class bdb.Breakpoint(self, file, line, temporary=False, 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
   "bpbynumber" and by "(file, line)" pairs through "bplist".  The
   former points to a single instance of 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 "file name" 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".

   "Breakpoint" instances have the following methods:

   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.

   enable()

      Mark the breakpoint as enabled.

   disable()

      Mark the breakpoint as disabled.

   bpformat()

      Return a string with all the information about the breakpoint,
      nicely formatted:

      * Breakpoint number.

      * Temporary status (del or keep).

      * File/line position.

      * Break condition.

      * Number of times to ignore.

      * Number of times hit.

      New in version 3.2.

   bpprint(out=None)

      Print the output of "bpformat()" to the file *out*, or if it is
      "None", to standard output.

   "Breakpoint" instances have the following attributes:

   file

      File name of the "Breakpoint".

   line

      Line number of the "Breakpoint" within "file".

   temporary

      True if a "Breakpoint" at (file, line) is temporary.

   cond

      Condition for evaluating a "Breakpoint" at (file, line).

   funcname

      Function name that defines whether a "Breakpoint" is hit upon
      entering the function.

   enabled

      True if "Breakpoint" is enabled.

   bpbynumber

      Numeric index for a single instance of a "Breakpoint".

   bplist

      Dictionary of "Breakpoint" instances indexed by ("file", "line")
      tuples.

   ignore

      Number of times to ignore a "Breakpoint".

   hits

      Count of the number of times a "Breakpoint" has been hit.

class bdb.Bdb(skip=None)

   The "Bdb" class 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 ("pdb.Pdb") is an example.

   The *skip* argument, if given, must be an iterable of glob-style
   module name patterns.  The debugger will not step into frames that
   originate in a module that matches one of these patterns. Whether a
   frame is considered to originate in a certain module is determined
   by the "__name__" in the frame globals.

   New in version 3.1: The *skip* argument.

   The following methods of "Bdb" normally don’t need to be
   overridden.

   canonic(filename)

      Return canonical form of *filename*.

      For real file names, the canonical form is an operating-system-
      dependent, "case-normalized" "absolute path". A *filename* with
      angle brackets, such as ""<stdin>"" generated in interactive
      mode, is returned unchanged.

   reset()

      Set the "botframe", "stopframe", "returnframe" and "quitting"
      attributes with values ready to start debugging.

   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 raised 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 "sys.settrace()" for more information
      on the trace function.  For more information on code and frame
      objects, refer to The standard type hierarchy.

   dispatch_line(frame)

      If the debugger should stop on the current line, invoke the
      "user_line()" method (which should be overridden in subclasses).
      Raise a "BdbQuit" exception if the "Bdb.quitting" flag is set
      (which can be set from "user_line()").  Return a reference to
      the "trace_dispatch()" method for further tracing in that scope.

   dispatch_call(frame, arg)

      If the debugger should stop on this function call, invoke the
      "user_call()" method (which should be overridden in subclasses).
      Raise a "BdbQuit" exception if the "Bdb.quitting" flag is set
      (which can be set from "user_call()").  Return a reference to
      the "trace_dispatch()" method for further tracing in that scope.

   dispatch_return(frame, arg)

      If the debugger should stop on this function return, invoke the
      "user_return()" method (which should be overridden in
      subclasses). Raise a "BdbQuit" exception if the "Bdb.quitting"
      flag is set (which can be set from "user_return()").  Return a
      reference to the "trace_dispatch()" method for further tracing
      in that scope.

   dispatch_exception(frame, arg)

      If the debugger should stop at this exception, invokes the
      "user_exception()" method (which should be overridden in
      subclasses). Raise a "BdbQuit" exception if the "Bdb.quitting"
      flag is set (which can be set from "user_exception()").  Return
      a reference to the "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.

   is_skipped_line(module_name)

      Return True if *module_name* matches any skip pattern.

   stop_here(frame)

      Return True if *frame* is below the starting frame in the stack.

   break_here(frame)

      Return True if there is an effective breakpoint for this line.

      Check whether a line or function breakpoint exists and is in
      effect.  Delete temporary breakpoints based on information from
      "effective()".

   break_anywhere(frame)

      Return True if any breakpoint exists for *frame*’s filename.

   Derived classes should override these methods to gain control over
   debugger operation.

   user_call(frame, argument_list)

      Called from "dispatch_call()" if a break might stop inside the
      called function.

   user_line(frame)

      Called from "dispatch_line()" when either "stop_here()" or
      "break_here()" returns "True".

   user_return(frame, return_value)

      Called from "dispatch_return()" when "stop_here()" returns
      "True".

   user_exception(frame, exc_info)

      Called from "dispatch_exception()" when "stop_here()" returns
      "True".

   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.

   set_step()

      Stop after one line of code.

   set_next(frame)

      Stop on the next line in or below the given frame.

   set_return(frame)

      Stop when returning from the given frame.

   set_until(frame, lineno=None)

      Stop when the line with the *lineno* greater than the current
      one is reached or when returning from current frame.

   set_trace([frame])

      Start debugging from *frame*.  If *frame* is not specified,
      debugging starts from caller’s frame.

   set_continue()

      Stop only at breakpoints or when finished.  If there are no
      breakpoints, set the system trace function to "None".

   set_quit()

      Set the "quitting" attribute to "True".  This raises "BdbQuit"
      in the next call to one of the "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.

   set_break(filename, lineno, temporary=False, cond=None, funcname=None)

      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
      "canonic()" method.

   clear_break(filename, lineno)

      Delete the breakpoints in *filename* and *lineno*.  If none were
      set, return an error message.

   clear_bpbynumber(arg)

      Delete the breakpoint which has the index *arg* in the
      "Breakpoint.bpbynumber".  If *arg* is not numeric or out of
      range, return an error message.

   clear_all_file_breaks(filename)

      Delete all breakpoints in *filename*.  If none were set, return
      an error message.

   clear_all_breaks()

      Delete all existing breakpoints.  If none were set, return an
      error message.

   get_bpbynumber(arg)

      Return a breakpoint specified by the given number.  If *arg* is
      a string, it will be converted to a number.  If *arg* is a non-
      numeric string, if the given breakpoint never existed or has
      been deleted, a "ValueError" is raised.

      New in version 3.2.

   get_break(filename, lineno)

      Return True if there is a breakpoint for *lineno* in *filename*.

   get_breaks(filename, lineno)

      Return all breakpoints for *lineno* in *filename*, or an empty
      list if none are set.

   get_file_breaks(filename)

      Return all breakpoints in *filename*, or an empty list if none
      are set.

   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.

   get_stack(f, t)

      Return a list of (frame, lineno) tuples in a stack trace, and a
      size.

      The most recently called frame is last in the list. The size is
      the number of frames below the frame where the debugger was
      invoked.

   format_stack_entry(frame_lineno, lprefix=': ')

      Return a string with information about a stack entry, which is a
      "(frame, lineno)" tuple.  The return string contains:

      * The canonical 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 *statement*, given as a string.

   run(cmd, globals=None, locals=None)

      Debug a statement executed via the "exec()" function.  *globals*
      defaults to "__main__.__dict__", *locals* defaults to *globals*.

   runeval(expr, globals=None, locals=None)

      Debug an expression executed via the "eval()" function.
      *globals* and *locals* have the same meaning as in "run()".

   runctx(cmd, globals, locals)

      For backwards compatibility.  Calls the "run()" method.

   runcall(func, /, *args, **kwds)

      Debug a single function call, and return its result.

Finally, the module defines the following functions:

bdb.checkfuncname(b, frame)

   Return True if 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 *frame*. 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 on its first executable line.

bdb.effective(file, line, frame)

   Return "(active breakpoint, delete temporary flag)" or "(None,
   None)" as the breakpoint to act upon.

   The *active breakpoint* is the first entry in "bplist" for the
   ("file", "line") (which must exist) that is "enabled", for which
   "checkfuncname()" is True, and that has neither a False "condition"
   nor positive "ignore" count.  The *flag*, meaning that a temporary
   breakpoint should be deleted, is False only when the "cond" cannot
   be evaluated (in which case, "ignore" count is ignored).

   If no such entry exists, then (None, None) is returned.

bdb.set_trace()

   Start debugging with a "Bdb" instance from caller’s frame.
