Modules/_dbmmodule.c / Modules/_gdbmmodule.c

Source:

cpython 3.14 @ ab2d84fe1023/Modules/_gdbmmodule.c ↗

dbm.gnu wraps the gdbm library, providing a persistent dict-like object backed by a .gdbm database file. It is one of several dbm backends selected by dbm.open.

Map

Lines	Symbol	Role
1-80	gdbm_open wrapper	gdbm.open(filename, flag, mode)
81-200	dbmobject_subscript	db[key] — fetch and db[key] = value — store
201-300	dbmobject_keys	Return list of all keys
301-400	dbmobject_delete	del db[key]
401-500	dbmobject_reorganize	Compact the database file
501-600	dbmobject_sync	Flush in-memory cache to disk

Reading

gdbm.open

// CPython: Modules/_gdbmmodule.c:88 dbmopen
static PyObject *
dbmopen(PyObject *module, PyObject *args)
{
    const char *name;
    const char *flags = "r";
    int         iflags = GDBM_READER;
    int         mode   = 0666;
    if (!PyArg_ParseTuple(args, "s|si:open", &name, &flags, &mode))
        return NULL;
    /* Map flag string to GDBM flag:
       'r' → GDBM_READER, 'w' → GDBM_WRITER,
       'c' → GDBM_WRCREAT, 'n' → GDBM_NEWDB */
    ...
    GDBM_FILE dp = gdbm_open(name, 0, iflags, mode, NULL);
    if (dp == NULL) {
        PyErr_SetFromErrnoWithFilenameObject(DbmError, PyTuple_GET_ITEM(args, 0));
        return NULL;
    }
    return newdbmobject(dp);
}

db[key] and db[key] = value

// CPython: Modules/_gdbmmodule.c:180 dbmobject_subscript
static PyObject *
dbmobject_subscript(dbmobject *dp, PyObject *key)
{
    datum drec, krec;
    if (!PyArg_Parse(key, "y*", &krec.dptr) ...) return NULL;
    drec = gdbm_fetch(dp->di_dbm, krec);
    if (drec.dptr == NULL) {
        PyErr_SetObject(PyExc_KeyError, key);
        return NULL;
    }
    PyObject *v = PyBytes_FromStringAndSize(drec.dptr, drec.dsize);
    free(drec.dptr);
    return v;
}

All keys and values are bytes. The datum struct holds a char * and a size_t.

keys()

// CPython: Modules/_gdbmmodule.c:280 dbm_keys
/* Iterates using gdbm_firstkey / gdbm_nextkey */
static PyObject *
dbm_keys(dbmobject *dp, PyObject *args)
{
    PyObject *v = PyList_New(0);
    datum key = gdbm_firstkey(dp->di_dbm);
    while (key.dptr) {
        PyList_Append(v, PyBytes_FromStringAndSize(key.dptr, key.dsize));
        datum nextkey = gdbm_nextkey(dp->di_dbm, key);
        free(key.dptr);
        key = nextkey;
    }
    return v;
}

reorganize

// CPython: Modules/_gdbmmodule.c:440 dbm_reorganize_impl
/* gdbm never shrinks the database file; reorganize() rewrites it compactly. */
static PyObject *
dbm_reorganize_impl(dbmobject *dp)
{
    if (gdbm_reorganize(dp->di_dbm) != 0) {
        PyErr_SetString(DbmError, gdbm_strerror(gdbm_errno));
        return NULL;
    }
    Py_RETURN_NONE;
}

gopy notes

dbm.gnu is in module/dbm/gnu/module.go. It uses cgo to call libgdbm. The gdbm.open API maps to gdbm_open(3) via C.gdbm_open. Key/value conversion uses C.GoBytes and C.CBytes. reorganize calls C.gdbm_reorganize.