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| -rw-r--r-- | Doc/library/pickle.rst | 71 |
1 files changed, 0 insertions, 71 deletions
diff --git a/Doc/library/pickle.rst b/Doc/library/pickle.rst index 6c2b269..cd50d11 100644 --- a/Doc/library/pickle.rst +++ b/Doc/library/pickle.rst @@ -266,11 +266,6 @@ The :mod:`pickle` module exports two classes, :class:`Pickler` and See :ref:`pickle-persistent` for details and examples of uses. - .. method:: clear_memo() - - Deprecated. Use the :meth:`clear` method on :attr:`memo`, instead. - Clear the pickler's memo, useful when reusing picklers. - .. attribute:: fast Deprecated. Enable fast mode if set to a true value. The fast mode @@ -281,12 +276,6 @@ The :mod:`pickle` module exports two classes, :class:`Pickler` and Use :func:`pickletools.optimize` if you need more compact pickles. - .. attribute:: memo - - Dictionary-like object holding previously pickled objects to allow - shared or recursive objects to pickled by reference as opposed to - by value. - .. class:: Unpickler(file, [\*, encoding="ASCII", errors="strict"]) @@ -332,12 +321,6 @@ The :mod:`pickle` module exports two classes, :class:`Pickler` and how they can be loaded, potentially reducing security risks. Refer to :ref:`pickle-restrict` for details. - .. attribute:: memo - - Dictionary-like object holding previously unpickled objects to allow - shared or recursive objects to unpickled by reference as opposed to - by value. - .. _pickle-picklable: @@ -735,60 +718,6 @@ The following example reads the resulting pickled data. :: data = pickle.load(f) -Reusing Pickler Instances -^^^^^^^^^^^^^^^^^^^^^^^^^ - -It is possible to make multiple calls to the :meth:`dump` method of the same -:class:`Pickler` instance. These must then be matched to the same number of -calls to the :meth:`load` method of the corresponding :class:`Unpickler` -instance. If the same object is pickled by multiple :meth:`dump` calls, the -:meth:`load` will all yield references to the same object. - -Please note, this is intended for pickling multiple objects without intervening -modifications to the objects or their parts. If you modify an object and then -pickle it again using the same :class:`Pickler` instance, the object is not -pickled again --- a reference to it is pickled and the :class:`Unpickler` will -return the old value, not the modified one. :: - - import io - import pickle - - data = {"hello": 0, "spam": 1} - - # Create a binary file-like object to which the Pickler instance will - # write the pickles. - f = io.BytesIO() - p = pickle.Pickler(f) - p.dump(data) - - # This second call appends a new pickle to the file. The modification we - # make is lost because objects are pickled by reference when seen again. - data["eggs"] = 2 - p.dump(data) - - # Now, we load the pickles saved in our file-like object. - f.seek(0) - u = pickle.Unpickler(f) - data1 = u.load() - data2 = u.load() - - if data1 is data2: - print("data1 and data2 are the same object") - else: - print("data1 and data2 are not the same object") - - if "eggs" in data2: - print("The modification was pickled.") - else: - print("The modification was not pickled.") - -Reusing a :class:`Pickler` instance like we shown can be a useful -optimization. For example, a multi-process application could use this feature -to reduce the size of the pickles transmitted across processes over time -(assuming the pickles exchanged are containers sharing common immutable -objects). However, you should take special care to regularly clear -:attr:``Pickler.memo`` and :attr:``Unpickler.memo`` to avoid memory-leaks. - .. XXX: Add examples showing how to optimize pickles for size (like using .. pickletools.optimize() or the gzip module). |