Here is a statistic for most called PyObject_INIT or PyObject_INIT_VAR for types (collected during running Python tests on 32-bit Linux). type count % acc.% builtin_function_or_method 116012007 36.29% 36.29% method 52465386 16.41% 52.70% int 42828741 13.40% 66.09% str 37017098 11.58% 77.67% generator 14026583 4.39% 82.06% list_iterator 8731329 2.73% 84.79% bytes 7217934 2.26% 87.04% tuple_iterator 5042563 1.58% 88.62% float 4672980 1.46% 90.08% set 3319699 1.04% 91.12% _io.StringIO 3000369 0.94% 92.06% str_iterator 2126838 0.67% 92.73% list 2031059 0.64% 93.36% dict 1691993 0.53% 93.89% method-wrapper 1573139 0.49% 94.38% function 1472062 0.46% 94.84% traceback 1388278 0.43% 95.28% tuple 1132071 0.35% 95.63% memoryview 1092173 0.34% 95.97% cell 1049496 0.33% 96.30% managedbuffer 1036889 0.32% 96.63% bytearray 711969 0.22% 96.85% range_iterator 496924 0.16% 97.00% range 483971 0.15% 97.15% super 472447 0.15% 97.30% map 449567 0.14% 97.44% frame 427320 0.13% 97.58% set_iterator 423392 0.13% 97.71% Leaf 398705 0.12% 97.83% symtable 374412 0.12% 97.95% Types for which free lists already are used: builtin_function_or_method, method, float, tuple, list, dict, frame. Some free list implementations (e.g. for tuple) don't call PyObject_INIT/PyObject_INIT_VAR. That is why numbers are such low for tuples. Perhaps it is worth to add free lists for other types: int, str, bytes, generator, list and tuple iterators? Shortened tables for variable-sized objects (that calls PyObject_INIT_VAR): int 42828741 13.40% 0 425353 0.99% 0.99% 1 21399290 49.96% 50.96% 2 10496856 24.51% 75.47% 3 4873346 11.38% 86.85% 4 1021563 2.39% 89.23% 5 1246444 2.91% 92.14% 6 733676 1.71% 93.85% 7 123074 0.29% 94.14% 8 139203 0.33% 94.47% ... bytes 7217934 2.26% 0 842 0.01% 0.01% 1 179469 2.49% 2.50% 2 473306 6.56% 9.06% 3 254968 3.53% 12.59% 4 1169164 16.20% 28.79% 5 72806 1.01% 29.79% 6 128668 1.78% 31.58% 7 169694 2.35% 33.93% 8 155154 2.15% 36.08% 9 67320 0.93% 37.01% 10 51703 0.72% 37.73% 11 42574 0.59% 38.32% 12 108947 1.51% 39.83% 13 40812 0.57% 40.39% 14 126783 1.76% 42.15% 15 37873 0.52% 42.67% 16 447482 6.20% 48.87% 17 194320 2.69% 51.56% 18 251685 3.49% 55.05% 19 159435 2.21% 57.26% 20 212521 2.94% 60.20% ... 31 18751 0.26% 67.32% 32 159781 2.21% 69.54% 33 8332 0.12% 69.65% ... 63 19841 0.27% 79.21% 64 144982 2.01% 81.22% 65 5216 0.07% 81.29% ... 127 1354 0.02% 85.44% 128 376539 5.22% 90.66% 129 17468 0.24% 90.90% ... 255 178 0.00% 92.39% 256 11993 0.17% 92.55% 257 124 0.00% 92.56% ...