Add pudb.b

[asmeurer]

This lets you just run

import pudb.b

to trigger a set_trace(). It works by monkey-patching
__builtins__.__import__. It does not yet work in Python 3.3, due to the new
import mechanism.

See #109.

[asmeurer]

How do we feel about the name pudb.b? I could also create a module pu.db, though I think we would have to literally install pu/db.py.

[inducer]

Will this work with PyPy?

[asmeurer]

Looks like it doesn't.

[asmeurer]

I changed it to use __builtin__.__dict__, but then I get

Traceback (most recent call last):
  File "app_main.py", line 72, in run_toplevel
  File "test.py", line 1, in <module>
    import pudb.b
  File "/Users/aaronmeurer/Documents/pudb/pudb/b.py", line 20, in <module>
    set_trace()
  File "/Users/aaronmeurer/Documents/pudb/pudb/b.py", line 16, in set_trace
    dbg = _get_debugger()
  File "/Users/aaronmeurer/Documents/pudb/pudb/__init__.py", line 34, in _get_debugger
    from pudb.debugger import Debugger
  File "/Users/aaronmeurer/Documents/pudb/pudb/b.py", line 8, in __myimport__
    return __origimport__(name, *args, **kwargs)
  File "/Users/aaronmeurer/Documents/pudb/pudb/debugger.py", line 5, in <module>
    import urwid
  File "/Users/aaronmeurer/Documents/pudb/pudb/b.py", line 8, in __myimport__
    return __origimport__(name, *args, **kwargs)
ImportError: No module named urwid

[inducer]

I'm not sure I'm a huge fan of this, but I'll merge it for the time being. I reserve the right to yank it out if we determine it's a bad idea. (Which it may be because of how deeply it has to reach into Python's guts...import hooks?) On the upside, the change is self-contained, so there isn't much risk here.

[asmeurer]

I do intend to make this work with Python 3. It's pretty useless to me if it doesn't work there.