Metaclass Recipe: Automatic Debugger Methods

Step 2

In this step, we will modify the get_debugger_func decorator to invoke the interactive debugger after printing the exception traceback.

Your task, once again, is to implement the __debugger__ metaclass.

import inspect, traceback, sys, pdb

def get_debugger_func(func):
    def new_func(*args):
        try:
            return func(*args)
        except Exception,e:
            traceback.print_exc()
            print '-'*80
            pdb.post_mortem(sys.exc_traceback)

    return new_func

class __debugger__(type):
    """Define this class"""

class Example(object):
    __metaclass__ = __debugger__

    def divide(self, v):
        # exception if v == 0
        result = 100 / v
        return result

    def interpolate(self, *args):
        # exception if len(args) != 2
        result = "%s is %s!" % args
        return result

if __name__ == '__main__':
    e = Example()

    print e.divide(0)

    print '-'*80

    print e.interpolate('Feihong', 'very', 'cool')

Expected output:

Traceback (most recent call last):
  File "D:\Projects\PyCon 2008 Talks\framework-tutorial\src\metaclass\debugger\solutions\debugger2.py", line 11, in new_func
    return func(*args)
  File "D:\Projects\PyCon 2008 Talks\framework-tutorial\src\metaclass\debugger\solutions\debugger2.py", line 33, in divide
    result = 100 / v
ZeroDivisionError: integer division or modulo by zero
--------------------------------------------------------------------------------
> d:\projects\pycon 2008 talks\framework-tutorial\src\metaclass\debugger\solutions\debugger2.py(33)divide()
-> result = 100 / v
(Pdb) c
None
--------------------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\Projects\PyCon 2008 Talks\framework-tutorial\src\metaclass\debugger\solutions\debugger2.py", line 11, in new_func
    return func(*args)
  File "D:\Projects\PyCon 2008 Talks\framework-tutorial\src\metaclass\debugger\solutions\debugger2.py", line 38, in interpolate
    result = "%s is %s!" % args
TypeError: not all arguments converted during string formatting
--------------------------------------------------------------------------------
> d:\projects\pycon 2008 talks\framework-tutorial\src\metaclass\debugger\solutions\debugger2.py(38)interpolate()
-> result = "%s is %s!" % args
(Pdb)

Hints

1. The solution to this step is very similar to the solution from the last step.
2. Actually, the definition of __debugger__ is completely identical. This was just a trick question to see if you were paying attention.

Solution: solutions/debugger2.py

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