Author: Carl Friedrich Bolz <cfb...@gmx.de> Branch: list-strategies Changeset: r47700:949dbd6aba1e Date: 2011-09-30 11:09 +0200 http://bitbucket.org/pypy/pypy/changeset/949dbd6aba1e/
Log: document the new behaviour 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 @@ -262,6 +262,26 @@ documented as such (as e.g. for hasattr()), in most cases PyPy lets the exception propagate instead. +Object Identity of Primitive Values, ``is`` and ``id`` +------------------------------------------------------- + +Object identity of primitive values works by value equality, not by identity of +the wrapper. This means that ``x + 1 is x + 1`` is always true, for arbitrary +integers ``x``. The rule applies for the following types: + + - ``int`` + + - ``float`` + + - ``long`` + + - ``complex`` + +This change requires some changes to ``id`` as well. ``id`` fulfills the +following condition: ``x is y <=> id(x) == id(y)``. Therefore ``id`` of the +above types will return a value that is computed from the argument, and can +thus be larger than ``sys.maxint`` (i.e. it can be an arbitrary long). + Miscellaneous ------------- @@ -284,14 +304,5 @@ never a dictionary as it sometimes is in CPython. Assigning to ``__builtins__`` has no effect. -* Do not compare immutable objects with ``is``. For example on CPython - it is true that ``x is 0`` works, i.e. does the same as ``type(x) is - int and x == 0``, but it is so by accident. If you do instead - ``x is 1000``, then it stops working, because 1000 is too large and - doesn't come from the internal cache. In PyPy it fails to work in - both cases, because we have no need for a cache at all. - -* Also, object identity of immutable keys in dictionaries is not necessarily - preserved. .. include:: _ref.txt _______________________________________________ pypy-commit mailing list pypy-commit@python.org http://mail.python.org/mailman/listinfo/pypy-commit
