[MERGE] Make cmd_branch check the destination before doing any I/O on the source.

[John Arbash Meinel]

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Michael Ellerman wrote:
> On Wed, 2006-07-26 at 10:48 +1000, Andrew Bennetts wrote:
>> On Tue, Jul 25, 2006 at 01:48:31PM -0500, John Arbash Meinel wrote:
>> [...]
>>> The only thing it really means is that if we get an exception, and then
>>> delete_tree() also raises, it will hide the original exception.
>>> The only way I know around it is:
>>>
>>> except Exception, e:
>>>   try:
>>>     to_transport.delete_tree('.')
>>>   except:
>>>     raise e
>>>   raise
>>>
>>> That will raise the original exception delete_tree() fails, though you
>>> lose the traceback. And if delete_tree() succeeds, it raises the
>>> original exception with the original traceback.
>> You can do slightly better with sys.exc_info():
>>
>> except Exception, e:
>>   exc_value, exc_type, exc_tb = sys.exc_info()
>>   try:
>>     to_transport.delete_tree('.')
>>   except:
>>     raise exc_value, exc_type, exc_tb
>>   raise
>>
>> This preserves the original exception, although the code is a bit uglier.
> 
> Could we wrap it in a function?
> 
> eg.
> 
> def execute_then_raise(callable, *args, **kwargs):
> 	exc_value, exc_type, exc_tb = sys.exc_info()
> 	try:
> 		callable(*args, **kwargs)
> 	except:
> 		pass
> 	raise exc_value, exc_type, exc_tb
> 
> 
> cheers
> 

It would seem that you should be able to. Though I wonder if it isn't
better to do:

def cleanup_then_raise(cleanup, *args, **kwargs):
	exc_value, exc_type, exc_tb = sys.exc_info()
	try:
		cleanup(*args, **kwargs)
	except:
		raise exc_value, exc_type, exc_tb
	raise

I would be okay with 'callable', but I think this makes it clearer when
we actually want to use the function.

John
=:->

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