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bpo-37409: fix relative import with no parent (#14956)

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Relative imports use resolve_name to get the absolute target name,
which first seeks the current module's absolute package name from the globals:
If __package__ (and __spec__.parent) are missing then
import uses __name__, truncating the last segment if
the module is a submodule rather than a package __init__.py
(which it guesses from whether __path__ is defined).

The __name__ attempt should fail if there is no parent package (top level modules),
if __name__ is '__main__' (-m entry points), or both (scripts).
That is, if both __name__ has no subcomponents and the module does not seem
to be a package __init__ module then import should fail.
This commit is contained in:
Ben Lewis 2019-09-11 20:09:47 +10:00 • committed by Brett Cannon
parent 6472ece5a0
commit 92420b3e67
5 changed files with 25 additions and 11 deletions
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24
Python/import.c
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@ -1646,23 +1646,20 @@ resolve_name(PyThreadState *tstate, PyObject *name, PyObject *globals, int level
if (dot == -2) {
goto error;
}
if (dot >= 0) {
PyObject *substr = PyUnicode_Substring(package, 0, dot);
if (substr == NULL) {
goto error;
}
Py_SETREF(package, substr);
else if (dot == -1) {
goto no_parent_error;
}
PyObject *substr = PyUnicode_Substring(package, 0, dot);
if (substr == NULL) {
goto error;
}
Py_SETREF(package, substr);
}
}
last_dot = PyUnicode_GET_LENGTH(package);
if (last_dot == 0) {
_PyErr_SetString(tstate, PyExc_ImportError,
"attempted relative import "
"with no known parent package");
goto error;
goto no_parent_error;
}
for (level_up = 1; level_up < level; level_up += 1) {
@ -1688,6 +1685,11 @@ resolve_name(PyThreadState *tstate, PyObject *name, PyObject *globals, int level
Py_DECREF(base);
return abs_name;
no_parent_error:
_PyErr_SetString(tstate, PyExc_ImportError,
"attempted relative import "
"with no known parent package");
error:
Py_XDECREF(package);
return NULL;