Objects/fileobject.c

Source:

cpython 3.14 @ ab2d84fe1023/Objects/fileobject.c ↗

Objects/fileobject.c is the thin C API layer for file objects. The actual file I/O implementation lives in Modules/_io/ (buffered/text I/O). This file provides the helpers used by C extension code and the interpreter itself.

Map

Lines	Symbol	Role
1-50	PyFile_FromFd	Wrap a raw file descriptor in a Python file object
51-100	PyFile_GetLine	Read one line (used by input())
101-160	PyFile_WriteString	Write a C string to a Python file object
161-220	PyFile_WriteObject	Write repr(obj) or str(obj) to a file
221-300	_PyObject_Print	Internal: print an object to a C FILE *

Reading

PyFile_FromFd

// CPython: Objects/fileobject.c:28 PyFile_FromFd
PyObject *
PyFile_FromFd(int fd, const char *name, const char *mode,
              int buffering, const char *encoding,
              const char *errors, const char *newline,
              int closefd)
{
    /* Equivalent to io.open(fd, mode, buffering, encoding, errors, newline, closefd) */
    PyObject *io = PyImport_ImportModule("_io");
    PyObject *open = PyObject_GetAttrString(io, "open");
    return PyObject_Call(open, args, kwargs);
}

PyFile_FromFd(1, "<stdout>", "w", -1, NULL, NULL, NULL, 0) creates Python's sys.stdout.

PyFile_GetLine

// CPython: Objects/fileobject.c:68 PyFile_GetLine
PyObject *
PyFile_GetLine(PyObject *f, int n)
{
    PyObject *result;
    if (n <= 0)
        result = PyObject_CallMethodNoArgs(f, &_Py_ID(readline));
    else
        result = PyObject_CallMethodOneArg(f, &_Py_ID(readline),
                                           PyLong_FromLong(n));
    /* Strip trailing newline if present */
    ...
    return result;
}

Used by the interactive interpreter and input() builtin.

PyFile_WriteString

// CPython: Objects/fileobject.c:115 PyFile_WriteString
int
PyFile_WriteString(const char *s, PyObject *f)
{
    if (f == NULL) {
        /* No file: print to stderr directly */
        fputs(s, stderr);
        return 0;
    }
    PyObject *str = PyUnicode_FromString(s);
    int res = PyFile_WriteObject(str, f, Py_PRINT_RAW);
    Py_DECREF(str);
    return res;
}

Used extensively in the interpreter for error messages and tracebacks.

PyFile_WriteObject

// CPython: Objects/fileobject.c:148 PyFile_WriteObject
int
PyFile_WriteObject(PyObject *v, PyObject *f, int flags)
{
    /* flags=0: use repr(); flags=Py_PRINT_RAW: use str() */
    PyObject *writer = PyObject_GetAttr(f, &_Py_ID(write));
    PyObject *value = (flags & Py_PRINT_RAW) ? PyObject_Str(v) : PyObject_Repr(v);
    PyObject *result = PyObject_CallOneArg(writer, value);
    ...
}

Py_PRINT_RAW is the flag used by print() — it calls str(), not repr().

_PyObject_Print

// CPython: Objects/fileobject.c:228 _PyObject_Print
int
_PyObject_Print(PyObject *op, FILE *fp, int flags)
{
    /* Write to a C FILE *: used for debug output, tracebacks to stderr */
    clearerr(fp);
    if (op == NULL) {
        fputs("<nil>", fp);
    } else {
        PyObject *s = (flags & Py_PRINT_RAW) ? PyObject_Str(op) : PyObject_Repr(op);
        fputs(PyUnicode_AsUTF8(s), fp);
        ...
    }
    return ferror(fp) ? -1 : 0;
}

gopy notes

PyFile_FromFd maps to io.OpenFd in gopy's _io module. sys.stdout/sys.stderr/sys.stdin are created from fds 1/2/0. PyFile_WriteString and PyFile_WriteObject are used by the traceback printer (vm/eval_unwind.go) to write to sys.stderr.