Hi all, when building Cython, it compiles a couple of its own modules. I was interested in what this brings for the separate parts of the compiler, so I used the compilation of Cython's compiled modules as benchmark and compiled the separate parts incrementally, using the latest CPython 3.7.0. Baseline, uncompiled Python run: real 0m14.972s user 0m14.565s sys 0m0.165s Compiling the parser: Cython/Compiler/Scanning.py Cython/Plex/Scanners.py Cython/Plex/Actions.py Cython/Compiler/Parsing.py real 0m13.614s user 0m13.320s sys 0m0.136s Additionally: Cython/Compiler/Visitor.py Cython/Compiler/FlowControl.py real 0m7.857s user 0m7.778s sys 0m0.074s Additionally: Cython/Compiler/Code.py Cython/StringIOTree.py real 0m7.356s user 0m7.068s sys 0m0.102s Only compiling the tree visitor and the control flow analysis: Cython/Compiler/Visitor.py Cython/Compiler/FlowControl.py real 0m9.029s user 0m8.899s sys 0m0.082s These are the current shared library sizes on my machine: 57040 Cython/Plex/Actions.cpython-37m-x86_64-linux-gnu.so 72592 Cython/StringIOTree.cpython-37m-x86_64-linux-gnu.so 78880 Cython/Runtime/refnanny.cpython-37m-x86_64-linux-gnu.so 86384 Cython/Plex/Scanners.cpython-37m-x86_64-linux-gnu.so 127952 Cython/Compiler/Pythran.cpython-37m-x86_64-linux-gnu.so 227480 Cython/Compiler/Scanning.cpython-37m-x86_64-linux-gnu.so 322136 Cython/Compiler/Visitor.cpython-37m-x86_64-linux-gnu.so 559864 Cython/Tempita/_tempita.cpython-37m-x86_64-linux-gnu.so 598712 Cython/Compiler/FlowControl.cpython-37m-x86_64-linux-gnu.so 902904 Cython/Compiler/Parsing.cpython-37m-x86_64-linux-gnu.so 1133176 Cython/Compiler/Code.cpython-37m-x86_64-linux-gnu.so 4167120 insgesamt This suggests that by only compiling the 6 modules of the scanner, parser, tree visitor and CFA, we get about half the binary sizes, but almost the same speed. One caveat: Being pure Python, Cython does not use all that many of its own language features, so other code might suffer more or less. I also tried lxml's main module, and it compiles about 7% slower when removing Code.so. Given that it's the biggest of the modules, that feels acceptable for me, so I removed Code, Pythran, Lexicon and StringIOTree from the list of compiled modules for now. Stefan