On 2016-08-08 4:18 PM, Guido van Rossum wrote:
I think Nick would be interested in understanding why this is the case. What does the decorator do that could be so expensive?
From the looks of it it doesn't do anything special. Although with @contextlib.contextmanager we have to instantiate a generator (the decorated one) and advance it in __enter__. So it's an extra object instantiation + extra code in __enter__ and __exit__. Anyways, Nick knows much more about that code.
Giampaolo, before experimenting with a C implementation, I suggest you to try to compile contextlib.py with Cython. I'll be surprised if you can make it more than 30-40% faster. And you won't get much faster than Cython when you code contextmanager in C by hand.
Also, we don't have slots for __enter__ and __exit__, so there is no way to avoid the attribute lookup.
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