cpython/Objects/structseq.c

/* Implementation helper: a struct that looks like a tuple.
   See timemodule and posixmodule for example uses.

   The structseq helper is considered an internal CPython implementation
   detail.  Docs for modules using structseqs should call them
   "named tuples" (be sure to include a space between the two
   words and add a link back to the term in Docs/glossary.rst).
*/

#include "Python.h"
#include "structmember.h"

static const char visible_length_key[] = "n_sequence_fields";
static const char real_length_key[] = "n_fields";
static const char unnamed_fields_key[] = "n_unnamed_fields";

/* Fields with this name have only a field index, not a field name.
   They are only allowed for indices < n_visible_fields. */
char *PyStructSequence_UnnamedField = "unnamed field";
_Py_IDENTIFIER(n_sequence_fields);
_Py_IDENTIFIER(n_fields);
_Py_IDENTIFIER(n_unnamed_fields);

#define VISIBLE_SIZE(op) Py_SIZE(op)
#define VISIBLE_SIZE_TP(tp) PyLong_AsSsize_t( \
                      _PyDict_GetItemId((tp)->tp_dict, &PyId_n_sequence_fields))

#define REAL_SIZE_TP(tp) PyLong_AsSsize_t( \
                      _PyDict_GetItemId((tp)->tp_dict, &PyId_n_fields))
#define REAL_SIZE(op) REAL_SIZE_TP(Py_TYPE(op))

#define UNNAMED_FIELDS_TP(tp) PyLong_AsSsize_t( \
                      _PyDict_GetItemId((tp)->tp_dict, &PyId_n_unnamed_fields))
#define UNNAMED_FIELDS(op) UNNAMED_FIELDS_TP(Py_TYPE(op))


PyObject *
PyStructSequence_New(PyTypeObject *type)
{
    PyStructSequence *obj;
    Py_ssize_t size = REAL_SIZE_TP(type), i;

    obj = PyObject_GC_NewVar(PyStructSequence, type, size);
    if (obj == NULL)
        return NULL;
    /* Hack the size of the variable object, so invisible fields don't appear
     to Python code. */
    Py_SIZE(obj) = VISIBLE_SIZE_TP(type);
    for (i = 0; i < size; i++)
        obj->ob_item[i] = NULL;

    return (PyObject*)obj;
}

void
PyStructSequence_SetItem(PyObject* op, Py_ssize_t i, PyObject* v)
{
    PyStructSequence_SET_ITEM(op, i, v);
}

PyObject*
PyStructSequence_GetItem(PyObject* op, Py_ssize_t i)
{
    return PyStructSequence_GET_ITEM(op, i);
}

static void
structseq_dealloc(PyStructSequence *obj)
{
    Py_ssize_t i, size;

    size = REAL_SIZE(obj);
    for (i = 0; i < size; ++i) {
        Py_XDECREF(obj->ob_item[i]);
    }
    PyObject_GC_Del(obj);
}

/*[clinic input]
class structseq "PyStructSequence *" "NULL"
[clinic start generated code]*/
/*[clinic end generated code: output=da39a3ee5e6b4b0d input=9d781c6922c77752]*/

#include "clinic/structseq.c.h"

/*[clinic input]
@classmethod
structseq.__new__ as structseq_new
    sequence as arg: object
    dict: object = NULL
[clinic start generated code]*/

static PyObject *
structseq_new_impl(PyTypeObject *type, PyObject *arg, PyObject *dict)
/*[clinic end generated code: output=baa082e788b171da input=9b44810243907377]*/
{
    PyObject *ob;
    PyStructSequence *res = NULL;
    Py_ssize_t len, min_len, max_len, i, n_unnamed_fields;

    arg = PySequence_Fast(arg, "constructor requires a sequence");

    if (!arg) {
        return NULL;
    }

    if (dict && !PyDict_Check(dict)) {
        PyErr_Format(PyExc_TypeError,
                     "%.500s() takes a dict as second arg, if any",
                     type->tp_name);
        Py_DECREF(arg);
        return NULL;
    }

    len = PySequence_Fast_GET_SIZE(arg);
    min_len = VISIBLE_SIZE_TP(type);
    max_len = REAL_SIZE_TP(type);
    n_unnamed_fields = UNNAMED_FIELDS_TP(type);

    if (min_len != max_len) {
        if (len < min_len) {
            PyErr_Format(PyExc_TypeError,
                "%.500s() takes an at least %zd-sequence (%zd-sequence given)",
                type->tp_name, min_len, len);
            Py_DECREF(arg);
            return NULL;
        }

        if (len > max_len) {
            PyErr_Format(PyExc_TypeError,
                "%.500s() takes an at most %zd-sequence (%zd-sequence given)",
                type->tp_name, max_len, len);
            Py_DECREF(arg);
            return NULL;
        }
    }
    else {
        if (len != min_len) {
            PyErr_Format(PyExc_TypeError,
                         "%.500s() takes a %zd-sequence (%zd-sequence given)",
                         type->tp_name, min_len, len);
            Py_DECREF(arg);
            return NULL;
        }
    }

    res = (PyStructSequence*) PyStructSequence_New(type);
    if (res == NULL) {
        Py_DECREF(arg);
        return NULL;
    }
    for (i = 0; i < len; ++i) {
        PyObject *v = PySequence_Fast_GET_ITEM(arg, i);
        Py_INCREF(v);
        res->ob_item[i] = v;
    }
    for (; i < max_len; ++i) {
        if (dict && (ob = PyDict_GetItemString(
            dict, type->tp_members[i-n_unnamed_fields].name))) {
        }
        else {
            ob = Py_None;
        }
        Py_INCREF(ob);
        res->ob_item[i] = ob;
    }

    Py_DECREF(arg);
    return (PyObject*) res;
}


static PyObject *
structseq_repr(PyStructSequence *obj)
{
    /* buffer and type size were chosen well considered. */
#define REPR_BUFFER_SIZE 512
#define TYPE_MAXSIZE 100

    PyTypeObject *typ = Py_TYPE(obj);
    Py_ssize_t i;
    int removelast = 0;
    Py_ssize_t len;
    char buf[REPR_BUFFER_SIZE];
    char *endofbuf, *pbuf = buf;

    /* pointer to end of writeable buffer; safes space for "...)\0" */
    endofbuf= &buf[REPR_BUFFER_SIZE-5];

    /* "typename(", limited to  TYPE_MAXSIZE */
    assert(TYPE_MAXSIZE < sizeof(buf));
    len = strlen(typ->tp_name);
    if (len <= TYPE_MAXSIZE) {
        strcpy(pbuf, typ->tp_name);
        pbuf += len;
    }
    else {
        strncpy(pbuf, typ->tp_name, TYPE_MAXSIZE);
        pbuf += TYPE_MAXSIZE;
    }
    *pbuf++ = '(';

    for (i=0; i < VISIBLE_SIZE(obj); i++) {
        PyObject *val, *repr;
        const char *cname, *crepr;

        cname = typ->tp_members[i].name;
        if (cname == NULL) {
            PyErr_Format(PyExc_SystemError, "In structseq_repr(), member %zd name is NULL"
                         " for type %.500s", i, typ->tp_name);
            return NULL;
        }
        val = PyStructSequence_GET_ITEM(obj, i);
        repr = PyObject_Repr(val);
        if (repr == NULL)
            return NULL;
        crepr = PyUnicode_AsUTF8(repr);
        if (crepr == NULL) {
            Py_DECREF(repr);
            return NULL;
        }

        /* + 3: keep space for "=" and ", " */
        len = strlen(cname) + strlen(crepr) + 3;
        if ((pbuf+len) <= endofbuf) {
            strcpy(pbuf, cname);
            pbuf += strlen(cname);
            *pbuf++ = '=';
            strcpy(pbuf, crepr);
            pbuf += strlen(crepr);
            *pbuf++ = ',';
            *pbuf++ = ' ';
            removelast = 1;
            Py_DECREF(repr);
        }
        else {
            strcpy(pbuf, "...");
            pbuf += 3;
            removelast = 0;
            Py_DECREF(repr);
            break;
        }
    }
    if (removelast) {
        /* overwrite last ", " */
        pbuf-=2;
    }
    *pbuf++ = ')';
    *pbuf = '\0';

    return PyUnicode_FromString(buf);
}

static PyObject *
structseq_reduce(PyStructSequence* self)
{
    PyObject* tup = NULL;
    PyObject* dict = NULL;
    PyObject* result;
    Py_ssize_t n_fields, n_visible_fields, n_unnamed_fields, i;

    n_fields = REAL_SIZE(self);
    n_visible_fields = VISIBLE_SIZE(self);
    n_unnamed_fields = UNNAMED_FIELDS(self);
    tup = PyTuple_New(n_visible_fields);
    if (!tup)
        goto error;

    dict = PyDict_New();
    if (!dict)
        goto error;

    for (i = 0; i < n_visible_fields; i++) {
        Py_INCREF(self->ob_item[i]);
        PyTuple_SET_ITEM(tup, i, self->ob_item[i]);
    }

    for (; i < n_fields; i++) {
        const char *n = Py_TYPE(self)->tp_members[i-n_unnamed_fields].name;
        if (PyDict_SetItemString(dict, n, self->ob_item[i]) < 0)
            goto error;
    }

    result = Py_BuildValue("(O(OO))", Py_TYPE(self), tup, dict);

    Py_DECREF(tup);
    Py_DECREF(dict);

    return result;

error:
    Py_XDECREF(tup);
    Py_XDECREF(dict);
    return NULL;
}

static PyMethodDef structseq_methods[] = {
    {"__reduce__", (PyCFunction)structseq_reduce, METH_NOARGS, NULL},
    {NULL, NULL}
};

static PyTypeObject _struct_sequence_template = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    NULL,                                       /* tp_name */
    sizeof(PyStructSequence) - sizeof(PyObject *), /* tp_basicsize */
    sizeof(PyObject *),                         /* tp_itemsize */
    (destructor)structseq_dealloc,              /* tp_dealloc */
    0,                                          /* tp_print */
    0,                                          /* tp_getattr */
    0,                                          /* tp_setattr */
    0,                                          /* tp_reserved */
    (reprfunc)structseq_repr,                   /* tp_repr */
    0,                                          /* tp_as_number */
    0,                                          /* tp_as_sequence */
    0,                                          /* tp_as_mapping */
    0,                                          /* tp_hash */
    0,                                          /* tp_call */
    0,                                          /* tp_str */
    0,                                          /* tp_getattro */
    0,                                          /* tp_setattro */
    0,                                          /* tp_as_buffer */
    Py_TPFLAGS_DEFAULT,                         /* tp_flags */
    NULL,                                       /* tp_doc */
    0,                                          /* tp_traverse */
    0,                                          /* tp_clear */
    0,                                          /* tp_richcompare */
    0,                                          /* tp_weaklistoffset */
    0,                                          /* tp_iter */
    0,                                          /* tp_iternext */
    structseq_methods,                          /* tp_methods */
    NULL,                                       /* tp_members */
    0,                                          /* tp_getset */
    0,                                          /* tp_base */
    0,                                          /* tp_dict */
    0,                                          /* tp_descr_get */
    0,                                          /* tp_descr_set */
    0,                                          /* tp_dictoffset */
    0,                                          /* tp_init */
    0,                                          /* tp_alloc */
    structseq_new,                              /* tp_new */
};

int
PyStructSequence_InitType2(PyTypeObject *type, PyStructSequence_Desc *desc)
{
    PyObject *dict;
    PyMemberDef* members;
    Py_ssize_t n_members, n_unnamed_members, i, k;
    PyObject *v;

#ifdef Py_TRACE_REFS
    /* if the type object was chained, unchain it first
       before overwriting its storage */
    if (type->ob_base.ob_base._ob_next) {
        _Py_ForgetReference((PyObject*)type);
    }
#endif

    n_unnamed_members = 0;
    for (i = 0; desc->fields[i].name != NULL; ++i)
        if (desc->fields[i].name == PyStructSequence_UnnamedField)
            n_unnamed_members++;
    n_members = i;

    memcpy(type, &_struct_sequence_template, sizeof(PyTypeObject));
    type->tp_base = &PyTuple_Type;
    type->tp_name = desc->name;
    type->tp_doc = desc->doc;

    members = PyMem_NEW(PyMemberDef, n_members-n_unnamed_members+1);
    if (members == NULL) {
        PyErr_NoMemory();
        return -1;
    }

    for (i = k = 0; i < n_members; ++i) {
        if (desc->fields[i].name == PyStructSequence_UnnamedField)
            continue;
        members[k].name = desc->fields[i].name;
        members[k].type = T_OBJECT;
        members[k].offset = offsetof(PyStructSequence, ob_item)
          + i * sizeof(PyObject*);
        members[k].flags = READONLY;
        members[k].doc = desc->fields[i].doc;
        k++;
    }
    members[k].name = NULL;

    type->tp_members = members;

    if (PyType_Ready(type) < 0)
        return -1;
    Py_INCREF(type);

    dict = type->tp_dict;
#define SET_DICT_FROM_SIZE(key, value)                          \
    do {                                                        \
        v = PyLong_FromSsize_t(value);                          \
        if (v == NULL)                                          \
            return -1;                                          \
        if (PyDict_SetItemString(dict, key, v) < 0) {           \
            Py_DECREF(v);                                       \
            return -1;                                          \
        }                                                       \
        Py_DECREF(v);                                           \
    } while (0)

    SET_DICT_FROM_SIZE(visible_length_key, desc->n_in_sequence);
    SET_DICT_FROM_SIZE(real_length_key, n_members);
    SET_DICT_FROM_SIZE(unnamed_fields_key, n_unnamed_members);

    return 0;
}

void
PyStructSequence_InitType(PyTypeObject *type, PyStructSequence_Desc *desc)
{
    (void)PyStructSequence_InitType2(type, desc);
}

PyTypeObject*
PyStructSequence_NewType(PyStructSequence_Desc *desc)
{
    PyTypeObject *result;

    result = (PyTypeObject*)PyType_GenericAlloc(&PyType_Type, 0);
    if (result == NULL)
        return NULL;
    if (PyStructSequence_InitType2(result, desc) < 0) {
        Py_DECREF(result);
        return NULL;
    }
    return result;
}

int _PyStructSequence_Init(void)
{
    if (_PyUnicode_FromId(&PyId_n_sequence_fields) == NULL
        || _PyUnicode_FromId(&PyId_n_fields) == NULL
        || _PyUnicode_FromId(&PyId_n_unnamed_fields) == NULL)
        return -1;

    return 0;
}