Catching all exceptions in Python

except Exception: vs except BaseException::

The difference between catching Exception and BaseException is that according to the exception hierarchy exception like SystemExit, KeyboardInterrupt and GeneratorExit will not be caught when using except Exception because they inherit directly from BaseException.

except: vs except BaseException::

The difference between this two is mainly in python 2 (AFAIK), and it’s only when using an old style class as an Exception to be raised, in this case only expression-less except clause will be able to catch the exception eg.

class NewStyleException(Exception): pass

try:
   raise NewStyleException
except BaseException:
   print "Caught"

class OldStyleException: pass

try:
   raise OldStyleException
except BaseException:
   print "BaseException caught when raising OldStyleException"
except:
   print "Caught"