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A number of places in the code base (notably ceval.c and frameobject.c) rely on mapping variable names to indices in the frame "locals plus" array (AKA fast locals), and thus opargs. Currently the compiler indirectly encodes that information on the code object as the tuples co_varnames, co_cellvars, and co_freevars. At runtime the dependent code must calculate the proper mapping from those, which isn't ideal and impacts performance-sensitive sections. This is something we can easily address in the compiler instead. This change addresses the situation by replacing internal use of co_varnames, etc. with a single combined tuple of names in locals-plus order, along with a minimal array mapping each to its kind (local vs. cell vs. free). These two new PyCodeObject fields, co_fastlocalnames and co_fastllocalkinds, are not exposed to Python code for now, but co_varnames, etc. are still available with the same values as before (though computed lazily). Aside from the (mild) performance impact, there are a number of other benefits: * there's now a clear, direct relationship between locals-plus and variables * code that relies on the locals-plus-to-name mapping is simpler * marshaled code objects are smaller and serialize/de-serialize faster Also note that we can take this approach further by expanding the possible values in co_fastlocalkinds to include specific argument types (e.g. positional-only, kwargs). Doing so would allow further speed-ups in _PyEval_MakeFrameVector(), which is where args get unpacked into the locals-plus array. It would also allow us to shrink marshaled code objects even further. https://bugs.python.org/issue43693 |
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| .. | ||
| NEWS.d | ||
| ACKS | ||
| coverity_model.c | ||
| gdbinit | ||
| HISTORY | ||
| indent.pro | ||
| Porting | ||
| python-config.in | ||
| python-config.sh.in | ||
| python-embed.pc.in | ||
| python-wing3.wpr | ||
| python-wing4.wpr | ||
| python-wing5.wpr | ||
| python.man | ||
| python.pc.in | ||
| README | ||
| README.AIX | ||
| README.coverity | ||
| README.valgrind | ||
| requirements-test.txt | ||
| SpecialBuilds.txt | ||
| stable_abi.txt | ||
| svnmap.txt | ||
| valgrind-python.supp | ||
| vgrindefs | ||
Python Misc subdirectory
========================
This directory contains files that wouldn't fit in elsewhere. Some
documents are only of historic importance.
Files found here
----------------
ACKS Acknowledgements
gdbinit Handy stuff to put in your .gdbinit file, if you use gdb
HISTORY News from previous releases -- oldest last
indent.pro GNU indent profile approximating my C style
NEWS News for this release (for some meaning of "this")
Porting Mini-FAQ on porting to new platforms
python-config.in Python script template for python-config
python.man UNIX man page for the python interpreter
python.pc.in Package configuration info template for pkg-config
python-wing*.wpr Wing IDE project file
README The file you're reading now
README.AIX Information about using Python on AIX
README.coverity Information about running Coverity's Prevent on Python
README.valgrind Information for Valgrind users, see valgrind-python.supp
SpecialBuilds.txt Describes extra symbols you can set for debug builds
svnmap.txt Map of old SVN revs and branches to hg changeset ids,
help history-digging
valgrind-python.supp Valgrind suppression file, see README.valgrind
vgrindefs Python configuration for vgrind (a generic pretty printer)