The attached script works in 2.6(.4) but not in 2.7(.3); the script cannot locate its own source code if invoked by relative path and work directory has changed. If line 8 uncommented, everything is fine due to caching. 

I think this is related to issue #4050 changes in inspect.py. 

~ kgabor$ python ./instest.py

None ./instest.py
Traceback (most recent call last):
  File "./instest.py", line 10, in <module>
    print inspect.getsourcefile(A), inspect.getfile(A),inspect.findsource(A)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/inspect.py", line 529, in findsource
    raise IOError('source code not available')
IOError: source code not available

~ kgabor$ pwd
/Users/kgabor

~ kgabor$ python /Users/kgabor/instest.py

/Users/kgabor/instest.py /Users/kgabor/instest.py (['import inspect\n', 'import os\n', '\n', 'class A:\n', ' def __init__(self):\n', '  self.a=1\n', '\n', '#print inspect.getsourcefile(A),inspect.getfile(A),inspect.findsource(A)\n', "os.chdir('/')\n", 'print inspect.getsourcefile(A), inspect.getfile(A),inspect.findsource(A)\n'], 3)