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bpo-33234 Improve list() pre-sizing for inputs with known lengths (no __length_hint__) #9846

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Merged
pablogsal merged 10 commits into from
Oct 28, 2018
Merged

bpo-33234 Improve list() pre-sizing for inputs with known lengths (no __length_hint__) #9846

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7602879
Improve list() pre-sizing for inputs with known lengths
pablogsal Apr 17, 2018
39a8757
Preallocate only when __len__ is available to avoid loss of performan…
pablogsal Oct 13, 2018
ab450b3
Fix NEWS entry and correct style
pablogsal Oct 15, 2018
717ca67
Use _PyObject_HasLen to check if the object has lenght to avoid overhead
pablogsal Oct 23, 2018
b678442
Simplify implementation and don't capture all expections on error
pablogsal Oct 23, 2018
b40bd62
Add assert and fix formatting
pablogsal Oct 25, 2018
3837486
Remove uneeded test modification
pablogsal Oct 25, 2018
b6ff7ce
Don't preallocate if list is modified when calling PyObject_Size
pablogsal Oct 26, 2018
e7f8c46
Improve readability in the error handling branch
pablogsal Oct 26, 2018
0a6c8ba
Capture only TypeError as suggested by Serhiy
pablogsal Oct 28, 2018
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Improve readability in the error handling branch
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@pablogsal
pablogsal committed Oct 26, 2018
commit e7f8c464258acf2e82278909fb5e1a792aa65dbf
6 changes: 2 additions & 4 deletions Objects/listobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2679,12 +2679,10 @@ list___init___impl(PyListObject *self, PyObject *iterable)
if (_PyObject_HasLen(iterable)) {
Py_ssize_t iter_len = PyObject_Size(iterable);
if (iter_len == -1) {
if (PyErr_ExceptionMatches(PyExc_Exception)) {
PyErr_Clear();
}
else {
if (!PyErr_ExceptionMatches(PyExc_Exception)) {
return -1;
}
PyErr_Clear();
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@vstinner vstinner Oct 28, 2018

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@pablogsal, @serhiy-storchaka: In a previous comment, I proposed to add an helper function to "probe" an object size: so move this code into a private helper function. Since the same code is used by PyObject_LengthHint(), it would now make sense, no?

See also iter_len() ... which is different.

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@serhiy-storchaka serhiy-storchaka Oct 28, 2018

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This code will be used just in two places and is not too complex. Adding yet one intermediate function will add a performance penalty for calling a function and checking its result, and will complicate the code. If this code will be used in more places, it can be refactored.

}
if (iter_len > 0 && self->ob_item == NULL
&& list_preallocate_exact(self, iter_len)) {
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