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v0.8.1
https://github.com/python/cpython
09 December 2020, 11:06:31 UTC
Revision 049039832da3d02592d680cebf71ab8a665a6564 authored by Antoine Pitrou on 10 June 2020, 20:37:21 UTC, committed by GitHub on 10 June 2020, 20:37:21 UTC 
[3.7] bpo-40895: Update weakref documentation to remove old warnings (GH-20687) (GH-20793)
 


The doccumentation at https://docs.python.org/3.10/library/weakref.html cautions that the `WeakKeyDictionary` and `WeakValueDictionary` are susceptible to the problem of dictionary mutation during iteration.

These notes present the user with a problem that has no easy solution.

I dug into the implementation and found that fortunately, Antoine Pitrou already addressed this challenge (10 years ago!) by introducing an `_IterationGuard` context manager to the implementation, which delays mutation while an iteration is in progress.

I asked for confirmation and @pitrou agreed that these notes could be removed:
https://github.com/python/cpython/commit/c1baa601e2b558deb690edfdf334fceee3b03327GH-commitcomment-39514438.
(cherry picked from commit 1642c0ef750f96664a98cadb09301d492098d2fb)

Co-authored-by: Daniel Fortunov <asqui@users.noreply.github.com>

Automerge-Triggered-By: @pitrou
1 parent 4b378ac
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Tip revision: 049039832da3d02592d680cebf71ab8a665a6564 authored by Antoine Pitrou on 10 June 2020, 20:37:21 UTC
[3.7] bpo-40895: Update weakref documentation to remove old warnings (GH-20687) (GH-20793)
Tip revision: 0490398
bitset.c 

/* Bitset primitives used by the parser generator */

#include "pgenheaders.h"
#include "bitset.h"

bitset
newbitset(int nbits)
{
    int nbytes = NBYTES(nbits);
    bitset ss = (char *)PyObject_MALLOC(sizeof(BYTE) *  nbytes);

    if (ss == NULL)
        Py_FatalError("no mem for bitset");

    ss += nbytes;
    while (--nbytes >= 0)
        *--ss = 0;
    return ss;
}

void
delbitset(bitset ss)
{
    PyObject_FREE(ss);
}

int
addbit(bitset ss, int ibit)
{
    int ibyte = BIT2BYTE(ibit);
    BYTE mask = BIT2MASK(ibit);

    if (ss[ibyte] & mask)
        return 0; /* Bit already set */
    ss[ibyte] |= mask;
    return 1;
}

#if 0 /* Now a macro */
int
testbit(bitset ss, int ibit)
{
    return (ss[BIT2BYTE(ibit)] & BIT2MASK(ibit)) != 0;
}
#endif

int
samebitset(bitset ss1, bitset ss2, int nbits)
{
    int i;

    for (i = NBYTES(nbits); --i >= 0; )
        if (*ss1++ != *ss2++)
            return 0;
    return 1;
}

void
mergebitset(bitset ss1, bitset ss2, int nbits)
{
    int i;

    for (i = NBYTES(nbits); --i >= 0; )
        *ss1++ |= *ss2++;
}
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