105 lines
3.5 KiB
Plaintext
105 lines
3.5 KiB
Plaintext
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PEP: 286
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Title: Enhanced Argument Tuples
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Version: $Revision$
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Last-Modified: $Date$
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Author: loewis@informatik.hu-berlin.de (Martin von Loewis)
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Status: Active
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Type: Standards Track
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Created: 3-Mar-2002
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Python-Version: 2.3
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Post-History:
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Abstract
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PyArg_ParseTuple is confronted with difficult memory management if
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an argument converter creates new memory. To deal with these
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cases, a specialized argument type is proposed.
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Problem description
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Today, argument tuples keep references to the function arguments,
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which are guaranteed to live as long as the argument tuple exists
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which is at least as long as the function call is being executed.
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In some cases, parsing an argument will allocate new memory, which
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is then to be released by the caller. This has two problems:
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1. In case of failure, the application cannot know what memory to
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release; most callers don't even know that they have the
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responsibility to release that memory. Example for this are
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the N converter (bug #416288) and the es# converter (bug
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#501716).
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2. Even for successful argument parsing, it is still inconvenient
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for the caller to be responsible for releasing the memory. In
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some cases, this is unnecessarily inefficient. For example,
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the es converter copies the conversion result into memory, even
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though there already is a string object that has the right
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contents.
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Proposed solution
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A new type 'argument tuple' is introduced. This type derives from
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tuple, adding an __dict__ member (at tp_dictoffset -4). Instances
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of this type might get the following attributes:
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- 'failobjects', a list of objects which need to be deallocated
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in case of success
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- 'okobjects', a list of object which will be released when the
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argument tuple is released
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To manage this type, the following functions will be added, and
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used appropriately in ceval.c and getargs.c:
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- PyArgTuple_New(int);
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- PyArgTuple_AddFailObject(PyObject*, PyObject*);
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- PyArgTuple_AddFailMemory(PyObject*, void*);
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- PyArgTuple_AddOkObject(PyObject*, PyObject*);
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- PyArgTuple_AddOkMemory(PyObject*, void*);
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- PyArgTuple_ClearFailed(PyObject*);
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When argument parsing fails, all fail objects will be released
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through Py_DECREF, and all fail memory will be released through
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PyMem_Free. If parsing succeeds, the references to the fail
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objects and fail memory are dropped, without releasing anything.
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When the argument tuple is released, all ok objects and memory
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will be released.
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If those functions are called with an object of a different type,
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a warning is issued and no further action is taken; usage of the
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affected converters without using argument tuples is deprecated.
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Affected converters
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The following converters will add fail memory and fail objects: N,
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es, et, es#, et# (unless memory is passed into the converter)
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New converters
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To simplify Unicode conversion, the e* converters are duplicated
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as E* converters (Es, Et, Es#, Et#). The usage of the E*
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converters is identical to that of the e* converters, except that
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the application will not need to manage the resulting memory.
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This will be implemented through registration of Ok objects with
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the argument tuple. The e* converters are deprecated.
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Copyright
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This document has been placed in the public domain.
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Local Variables:
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mode: indented-text
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indent-tabs-mode: nil
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fill-column: 70
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End:
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