Python/ceval.c (part 27)

Source:

cpython 3.14 @ ab2d84fe1023/Python/ceval.c ↗

This annotation covers import opcodes. See python_ceval26_detail for function construction opcodes.

Map

Lines	Symbol	Role
1-80	IMPORT_NAME	Execute import foo.bar via __import__
81-180	IMPORT_FROM	from foo import bar — attribute access on module
181-280	IMPORT_STAR	from foo import * — copy to local namespace
281-420	__import__ protocol	Entry point for the import machinery
421-500	LOAD_BUILD_CLASS	class statement: load __build_class__

Reading

IMPORT_NAME

// CPython: Python/ceval.c:5380 IMPORT_NAME
inst(IMPORT_NAME, (fromlist, level -- res)) {
    PyObject *name = GETITEM(names, oparg);
    PyObject *import_func = _PyDict_GetItemWithError(f->f_builtins, &_Py_ID(__import__));
    /* __import__(name, globals, locals, fromlist, level) */
    res = PyObject_CallFunctionObjArgs(import_func,
                                       name, f->f_globals, f->f_locals,
                                       fromlist, level, NULL);
}

import os compiles to LOAD_CONST 0 (level) + LOAD_CONST None (fromlist) + IMPORT_NAME 'os'. The __import__ function looks up sys.modules first (fast path), then calls importlib._bootstrap._find_and_load.

IMPORT_FROM

// CPython: Python/ceval.c:5460 IMPORT_FROM
inst(IMPORT_FROM, (from -- from, res)) {
    PyObject *name = GETITEM(names, oparg);
    /* Try module's __dict__ first */
    res = PyObject_GetAttr(from, name);
    if (res == NULL && PyErr_ExceptionMatches(PyExc_ImportError)) {
        /* Provide better error message */
        PyErr_Format(PyExc_ImportError,
            "cannot import name %R from %R (%R)",
            name, from->ma_dict ? PyDict_GetItem(from->ma_dict, &_Py_ID(__name__)) : Py_None,
            ...);
    }
}

from os import path compiles to IMPORT_NAME 'os' + IMPORT_FROM 'path'. The IMPORT_FROM opcode calls getattr(os_module, 'path'). The error message includes the module name and file path for diagnostics.

IMPORT_STAR

// CPython: Python/ceval.c:5520 IMPORT_STAR
inst(IMPORT_STAR, (from --)) {
    PyObject *all = PyObject_GetAttr(from, &_Py_ID(__all__));
    if (all == NULL) {
        /* No __all__: import all names not starting with _ */
        PyObject *dict = PyObject_GetAttr(from, &_Py_ID(__dict__));
        for each name in dict.keys():
            if name[0] != '_':
                PyDict_SetItem(LOCALS(), name, dict[name]);
    } else {
        for each name in all:
            PyDict_SetItem(LOCALS(), name, getattr(from, name));
    }
    Py_XDECREF(all);
    Py_DECREF(from);
}

from foo import * copies names from foo.__all__ (or all non-underscore names) into the current namespace. This is why import * is discouraged: it silently overrides existing names and pollutes the namespace.

gopy notes

IMPORT_NAME is vm.ImportName in vm/eval_import.go. It calls module/builtins.Import. IMPORT_FROM calls objects.GetAttr. IMPORT_STAR checks __all__ via objects.GetAttr and uses objects.DictSetItem for each name. LOAD_BUILD_CLASS pushes builtins.__build_class__.