[Python-Dev] [numpy wishlist] Interpreter support for temporary elision in third-party classes (original) (raw)

Nikolaus Rath Nikolaus at rath.org
Fri Jun 6 04:27:20 CEST 2014

Nathaniel Smith <njs at pobox.com> writes:

> tmp1 = a + b > tmp1 += c > tmp1 /= c > result = tmp1

Could this transformation be done in the ast? And would that help? I don't think it could be done in the ast because I don't think you can work with anonymous temporaries there. But, now that you mention it, it could be done on the fly in the implementation of the relevant opcodes. I.e., BINADD could do if (PyREFCNT(left) == 1) result = PyNumberInPlaceAdd(left, right); else result = PyNumberAdd(left, right) Upside: all packages automagically benefit! Potential downsides to consider: - Subtle but real and user-visible change in Python semantics. I'd be a little nervous about whether anyone has implemented, say, an iadd with side effects such that you can tell whether a copy was made, even if the object being copied is immediately destroyed. Maybe this doesn't make sense though.

Hmm. I don't think this is as unlikely as it may sound. Consider eg the h5py module:

with h5py.File('database.h5') as fh: result = fh['key'] + np.ones(42)

if this were transformed to

with h5py.File('database.h5') as fh: tmp = fh['key'] tmp += np.ones(42) result = tmp

then the database.h5 file would get modified, and result would be of type h5py.Dataset rather than np.array.

Best, -Nikolaus

-- GPG encrypted emails preferred. Key id: 0xD113FCAC3C4E599F Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F

         »Time flies like an arrow, fruit flies like a Banana.«

More information about the Python-Dev mailing list