Objects/filterobject.c

Source:

cpython 3.14 @ ab2d84fe1023/Objects/filterobject.c ↗

Objects/filterobject.c implements the filter built-in. A filterobject wraps a predicate callable and an iterator, and yields only the elements for which the predicate returns a truthy value. When the predicate is None, it uses the element's own truthiness.

Map

Lines	Symbol	Role
1-50	filterobject, filter_new	Struct and constructor; stores func and it
51-110	filter_next	Pull from iterator, test predicate, repeat
111-150	filter_reduce, PyFilter_Type	Pickle support and type slot wiring

Reading

filterobject construction

filter_new calls PyObject_GetIter(seq) to get an iterator from the second argument, then stores both the predicate and the iterator on the object.

// Objects/filterobject.c:1 filterobject
typedef struct {
    PyObject_HEAD
    PyObject *func;
    PyObject *it;
} filterobject;

// Objects/filterobject.c:20 filter_new_impl
static PyObject *
filter_new_impl(PyTypeObject *type, PyObject *func, PyObject *iterable)
{
    PyObject *it = PyObject_GetIter(iterable);
    if (it == NULL) return NULL;
    filterobject *lz = PyObject_GC_New(filterobject, type);
    lz->func = Py_NewRef(func);
    lz->it   = it;
    return (PyObject *)lz;
}

filter_next: predicate loop

filter_next loops until the wrapped iterator is exhausted. For each element it either calls func(item) or, when func is None or Py_None, tests the element directly with PyObject_IsTrue.

// Objects/filterobject.c:51 filter_next
static PyObject *
filter_next(filterobject *lz)
{
    for (;;) {
        PyObject *item = (*Py_TYPE(lz->it)->tp_iternext)(lz->it);
        if (item == NULL) return NULL;
        int ok;
        if (lz->func == Py_None || lz->func == NULL) {
            ok = PyObject_IsTrue(item);
        } else {
            PyObject *good = PyObject_CallOneArg(lz->func, item);
            if (good == NULL) { Py_DECREF(item); return NULL; }
            ok = PyObject_IsTrue(good);
            Py_DECREF(good);
        }
        if (ok > 0) return item;
        Py_DECREF(item);
        if (ok < 0) return NULL;
    }
}

Pickle support

filter_reduce returns a tuple (filter, (func, it)) that recreates the filter by passing func and a reconstructed iterator. This mirrors the pattern used by map and zip.

gopy notes

Not yet ported. The planned package path is objects/filter.go. The Go version would hold a py.Object predicate and a py.Iterator, with Next() implementing the same predicate loop.