Author: Armin Rigo <ar...@tunes.org> Branch: Changeset: r87177:2b6a25a67d6b Date: 2016-09-17 10:48 +0200 http://bitbucket.org/pypy/pypy/changeset/2b6a25a67d6b/
Log: Document sys.getsizeof() diff --git a/pypy/doc/cpython_differences.rst b/pypy/doc/cpython_differences.rst --- a/pypy/doc/cpython_differences.rst +++ b/pypy/doc/cpython_differences.rst @@ -449,6 +449,27 @@ support (see ``multiline_input()``). On the other hand, ``parse_and_bind()`` calls are ignored (issue `#2072`_). +* ``sys.getsizeof()`` always raises ``TypeError``. This is because a + memory profiler using this function is most likely to give results + inconsistent with reality on PyPy. It would be possible to have + ``sys.getsizeof()`` return a number (with enough work), but that may + or may not represent how much memory the object uses. It doesn't even + make really sense to ask how much *one* object uses, in isolation with + the rest of the system. For example, instances have maps, which are + often shared across many instances; in this case the maps would + probably be ignored by an implementation of ``sys.getsizeof()``, but + their overhead is important in some cases if they are many instances + with unique maps. Conversely, equal strings may share their internal + string data even if they are different objects---or empty containers + may share parts of their internals as long as they are empty. Even + stranger, some lists create objects as you read them; if you try to + estimate the size in memory of ``range(10**6)`` as the sum of all + items' size, that operation will by itself create one million integer + objects that never existed in the first place. Note that some of + these concerns also exist on CPython, just less so. For this reason + we explicitly don't implement ``sys.getsizeof()``. + + .. _`is ignored in PyPy`: http://bugs.python.org/issue14621 .. _`little point`: http://events.ccc.de/congress/2012/Fahrplan/events/5152.en.html .. _`#2072`: https://bitbucket.org/pypy/pypy/issue/2072/ _______________________________________________ pypy-commit mailing list pypy-commit@python.org https://mail.python.org/mailman/listinfo/pypy-commit
