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[Python-Dev] [numpy wishlist] Interpreter support for temporaryelision in third-party classes
Nikolaus RathNikolaus 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., BIN_ADD could do>> if (Py_REFCNT(left) == 1)> result = PyNumber_InPlaceAdd(left, right);> else> result = PyNumber_Add(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 theh5py module:with h5py.File('database.h5') as fh: result = fh['key'] + np.ones(42)if this were transformed towith h5py.File('database.h5') as fh: tmp = fh['key'] tmp += np.ones(42) result = tmpthen the database.h5 file would get modified, *and* result would be oftype h5py.Dataset rather than np.array.Best,-Nikolaus-- GPG encrypted emails preferred. Key id: 0xD113FCAC3C4E599FFingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F »Time flies like an arrow, fruit flies like a Banana.«
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