Python/ceval.c (part 57)

Source:

cpython 3.14 @ ab2d84fe1023/Python/ceval.c ↗

This annotation covers import opcodes. See python_import8_detail for the import machinery internals.

Map

Lines	Symbol	Role
1-80	IMPORT_NAME	Execute import foo or from foo import ...
81-160	IMPORT_FROM	Extract an attribute after IMPORT_NAME
161-240	IMPORT_STAR	from module import *
241-360	Relative import	from . import foo, from .. import bar
361-500	LOAD_FROM_DICT_OR_GLOBALS	Conditional name lookup for class scope

Reading

IMPORT_NAME

// CPython: Python/ceval.c:5820 IMPORT_NAME
inst(IMPORT_NAME, (level, fromlist -- res)) {
    PyObject *name = GETITEM(FRAME_CO_NAMES, oparg);
    res = import_name(tstate, frame, name, fromlist, level);
    DECREF_INPUTS();
    ERROR_IF(res == NULL, error);
    DISPATCH();
}

static PyObject *
import_name(PyThreadState *tstate, _PyInterpreterFrame *frame,
            PyObject *name, PyObject *fromlist, PyObject *level)
{
    /* Call __import__(name, globals, locals, fromlist, level) */
    PyObject *import_func = _PyObject_GetAttrId(builtins, &PyId___import__);
    return PyObject_CallFunctionObjArgs(import_func, name, globals, locals,
                                        fromlist, level, NULL);
}

import foo.bar compiles to LOAD_CONST 0 (level 0), LOAD_CONST None (fromlist), IMPORT_NAME 'foo.bar'. The level encodes relative imports: 1 = current package, 2 = parent package.

IMPORT_FROM

// CPython: Python/ceval.c:5880 IMPORT_FROM
inst(IMPORT_FROM, (from -- from, res)) {
    PyObject *name = GETITEM(FRAME_CO_NAMES, oparg);
    res = import_from(tstate, from, name);
    ERROR_IF(res == NULL, error);
    DISPATCH();
}

static PyObject *
import_from(PyThreadState *tstate, PyObject *v, PyObject *name)
{
    /* Try getattr first, then look in __all__/__dict__ for star import */
    PyObject *x = PyObject_GetAttr(v, name);
    if (x != NULL) return x;
    ...
}

from foo import bar compiles to IMPORT_NAME 'foo', IMPORT_FROM 'bar', STORE_NAME 'bar', POP_TOP. IMPORT_FROM leaves the module on the stack so multiple names can be imported from it.

IMPORT_STAR

// CPython: Python/ceval.c:5940 IMPORT_STAR
inst(IMPORT_STAR, (from --)) {
    /* Copy names from module into the current namespace.
       Uses __all__ if defined, else all names not starting with '_'. */
    PyObject *locals = LOCALS();
    int err = import_all_from(tstate, locals, from);
    Py_DECREF(from);
    ERROR_IF(err != 0, error);
    DISPATCH();
}

from module import * is discouraged because it pollutes the namespace and makes it hard to trace where names come from. In a function scope, IMPORT_STAR is a SyntaxError because local variable analysis needs to know names at compile time.

gopy notes

IMPORT_NAME is in vm/eval_import.go. It calls vm.ImportName which goes through the __import__ hook. IMPORT_FROM calls objects.GetAttr. IMPORT_STAR calls vm.ImportStar which iterates module.__all__ or the module dict's keys.