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Modular Python Debugger

Project description

This is a rewrite of the Python debugger, (, itself a derivative of the stock Python debugger pdb.

This code makes assumes Python in the version range of 2.5 up to and not including 3K. Use pydb for Python 2.5 and earlier.

Some of the core routines include handling code stepping, implementing breakpoints (setting/removing them and checking whether one has occurred), and registering/unregistering a code to be debugged. The intention is that IDE frameworks like Eclipse, Aptana or Netbeans and alternative Python implementation should be able to use pieces of the debugger as they see fit.

The command API portion of the debugger is largely modeled on the GNU GDB model. A command-line interface (CLI) is provided as well as code for remote debugging

There’s a lot of cool stuff here that’s not in pydb.

  • Syntax colorization of source code and use of terminal highlighting Of course, this can be turned off.

  • out-of-process debugging. You can now debug your program in a different process or even a different computer on a different network

  • Better stepping granularity. Sometimes you want small steps, and sometimes large stepping. This fundamental issue is handled in a couple ways:

    • step+, step-, next+, next- commands. These force stepping/nexting to a different line. “set different” does this globally.
    • step>, step<, step!, next>, etc commands. Set the next step event to be something other than a “line” event such as a call, return or exception
    • one can set a filter set. If you just want to stop at line events (which is largely what you happens in pdb) you can. If however you just want to stop at calls and returns, and exceptions you can. Or pick some combination.
    • “set skip”. Ths cause statements I think you usually want to skip over such as function and class definition statement. This is turned on by default, but if you do want to stop here and get the full story you can.
  • In conjunction with handling all events by default, the event status is shown when stopped. The reason for stopping is also available via “info program”.

  • event tracing of calls and returns. I’m not sure why this was not done before. Probably because of the lack of the ability to set and move by different granularities, tracing calls and returns lead to too many unintersting stops (such as at the same place you just were at). Also, stopping on function definitions probably also added to this tedium.

    Because we are really handling return events, we can show you the return value. (pdb has an undocumented “retval” command that in fact doesn’t work.)

  • We do more in the way of looking at the bytecodes to give better information. Through this we can provide:

    • a “skip” command. It is like the “jump” command, but you don’t have to deal with line numbers. Sorry, no “hop” command yet.
    • disassembly of code fragments. You can now disassemble relative to the stack frames you are currently stopped at.
    • Better interpretation of where you are when inside execfile or exec. (But really though this is probably a Python compiler misfeature.)
    • Check that breakpoints are set only where they make sense (via magic in the package “coverage”.)
    • A more accurate determination of if you are at a function-defining “def” statement (because the caller instruction contains “MAKE_FUNCTION”.)
  • Debugger command arguments can be variables

Commands that take integer arguments like “up” “list” or “disassemble” allow you to use a Python expression including local or global variables that evaluates to an integer.

  • egg installable.

  • Debugger plays nice with other trace hooks. You can have several debugger objects.

  • These don’t directly effect end-users, but if you are developing the code they do. And keeping developers happy is a good thing. TM

    • more modulular.

      o Commands and subcommands are individual classes now, not methods

      in a class. This means they now have properties like the context in which they can be run, minimum abbreviation name or alias names. To add a new command you basically add a file in a directory.

      o I/O is it’s own layer. This simplifies interactive readline

      behavior from reading commands over a TCP socket.

      o An interface is it’s own layer. Local debugging, remote

      debugging, running debugger commands from a file (“source”) are different interfaces. This means, for example, that we are able to give better error reporting if a debugger command file has an error.

    • more testable. Much more unit and functional tests. More of pydb’s integration test will eventually be added.

Of course, I think pydb has a number of cool things that are not in the stock Python debugger, pdb. See for details.

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