Modules/_csv.c (part 7)

Source:

cpython 3.14 @ ab2d84fe1023/Modules/_csv.c ↗

This annotation covers the writer side and dialect management. See modules_csv6_detail for csv.reader, the row parser, and quoting modes.

Map

Lines	Symbol	Role
1-80	csv.writer	Create a writer object bound to a file
81-180	Writer.writerow	Format one row and write to the underlying file
181-260	Writer.writerows	Iterate and call writerow for each
261-360	Dialect validation	Check quotechar, delimiter, lineterminator constraints
361-500	csv.register_dialect / csv.unregister_dialect	Global dialect registry

Reading

Writer.writerow

// CPython: Modules/_csv.c:820 csv_writerow
static PyObject *
csv_writerow(WriterObj *self, PyObject *seq)
{
    DialectObj *dialect = self->dialect;
    PyObject *iter = PyObject_GetIter(seq);
    while (1) {
        PyObject *field = PyIter_Next(iter);
        if (field == NULL) break;
        /* Determine quoting */
        int want_escape = 0;
        PyObject *str = PyObject_Str(field);
        /* Check if str contains delimiter or quotechar */
        if (csv_join_append(self, str, ...) < 0) goto err;
        Py_DECREF(str);
        Py_DECREF(field);
    }
    /* append lineterminator and write to writer */
    PyObject *line = _csvwriter_join_reset(self);
    return PyObject_CallMethodOneArg(self->writeline, _Py_ID(write), line);
}

writerow stringifies each field with str(), escapes/quotes as required by the dialect, and writes the assembled line to the file object's write method. Non-string values are converted before quoting checks.

Dialect validation

// CPython: Modules/_csv.c:420 dialect_check_quoting
static int
dialect_check_quoting(int quoting)
{
    const StyleDesc *qs;
    for (qs = quote_styles; qs->name; qs++) {
        if ((int)qs->style == quoting) return 0;
    }
    PyErr_Format(PyExc_TypeError, "bad \"quoting\" value");
    return -1;
}

// CPython: Modules/_csv.c:360 dialect_check_char
static int
dialect_check_char(const char *name, Py_UCS4 c, PyObject *src, bool allow_none)
{
    if (c == 0 && !allow_none) {
        PyErr_Format(PyExc_TypeError, "\"%s\" must be a 1-character string", name);
        return -1;
    }
    if (c >= 128) {
        PyErr_Format(PyExc_TypeError,
            "\"%s\" must be a 1-character string", name);
        return -1;
    }
    return 0;
}

The delimiter and quotechar must be single ASCII characters. lineterminator can be multi-character ('\r\n'). quoting must be one of QUOTE_ALL, QUOTE_MINIMAL, QUOTE_NONNUMERIC, or QUOTE_NONE.

csv.register_dialect

// CPython: Modules/_csv.c:1020 csv_register_dialect
static PyObject *
csv_register_dialect(PyObject *module, PyObject *const *args, Py_ssize_t nargs,
                     PyObject *kwnames)
{
    /* csv.register_dialect(name, dialect=None, **fmtparams) */
    PyObject *name;
    PyObject *dialect_inst = dialect_new(&DialectType, args, kwnames);
    if (dialect_inst == NULL) return NULL;
    return PyDict_SetItem(get_dialects_dict(module), name, dialect_inst);
}

csv.register_dialect('pipes', delimiter='|', quoting=csv.QUOTE_NONE) stores a Dialect object in the module-level dialect registry dict. csv.reader(f, 'pipes') looks up the dialect by name.

gopy notes

csv.writer is module/csv.NewWriter in module/csv/module.go. writerow calls objects.Str on each field and appends to a strings.Builder. register_dialect stores dialects in module/csv.dialects (a map[string]*Dialect). dialect_check_char validates via len(rune) == 1 && rune < 128.