bpo-37645: add new function _PyObject_FunctionStr() (GH-14890)

Additional note: the `method_check_args` function in `Objects/descrobject.c` is written in such a way that it applies to all kinds of descriptors. In particular, a future re-implementation of `wrapper_descriptor` could use that code.

CC @vstinner @encukou 


https://bugs.python.org/issue37645



Automerge-Triggered-By: @encukou

Doc/c-api/object.rst

@@ -196,6 +196,7 @@ Object Protocol
       This function now includes a debug assertion to help ensure that it
       does not silently discard an active exception.
 
+
 .. c:function:: PyObject* PyObject_Bytes(PyObject *o)
 
    .. index:: builtin: bytes

Include/cpython/object.h

@@ -348,6 +348,7 @@ static inline void _Py_Dealloc_inline(PyObject *op)
 }
 #define _Py_Dealloc(op) _Py_Dealloc_inline(op)
 
+PyAPI_FUNC(PyObject *) _PyObject_FunctionStr(PyObject *);
 
 /* Safely decref `op` and set `op` to `op2`.
  *

Lib/test/test_call.py

@@ -74,7 +74,7 @@ class CFunctionCallsErrorMessages(unittest.TestCase):
         self.assertRaisesRegex(TypeError, msg, bool, x=2)
 
     def test_varargs4_kw(self):
-        msg = r"^index\(\) takes no keyword arguments$"
+        msg = r"^list[.]index\(\) takes no keyword arguments$"
         self.assertRaisesRegex(TypeError, msg, [].index, x=2)
 
     def test_varargs5_kw(self):
@@ -90,19 +90,19 @@ class CFunctionCallsErrorMessages(unittest.TestCase):
         self.assertRaisesRegex(TypeError, msg, next, x=2)
 
     def test_varargs8_kw(self):
-        msg = r"^pack\(\) takes no keyword arguments$"
+        msg = r"^_struct[.]pack\(\) takes no keyword arguments$"
         self.assertRaisesRegex(TypeError, msg, struct.pack, x=2)
 
     def test_varargs9_kw(self):
-        msg = r"^pack_into\(\) takes no keyword arguments$"
+        msg = r"^_struct[.]pack_into\(\) takes no keyword arguments$"
         self.assertRaisesRegex(TypeError, msg, struct.pack_into, x=2)
 
     def test_varargs10_kw(self):
-        msg = r"^index\(\) takes no keyword arguments$"
+        msg = r"^deque[.]index\(\) takes no keyword arguments$"
         self.assertRaisesRegex(TypeError, msg, collections.deque().index, x=2)
 
     def test_varargs11_kw(self):
-        msg = r"^pack\(\) takes no keyword arguments$"
+        msg = r"^Struct[.]pack\(\) takes no keyword arguments$"
         self.assertRaisesRegex(TypeError, msg, struct.Struct.pack, struct.Struct(""), x=2)
 
     def test_varargs12_kw(self):

Lib/test/test_descr.py

@@ -1967,7 +1967,7 @@ order (MRO) for bases """
         # different error messages.
         set_add = set.add
 
-        expected_errmsg = "descriptor 'add' of 'set' object needs an argument"
+        expected_errmsg = "unbound method set.add() needs an argument"
 
         with self.assertRaises(TypeError) as cm:
             set_add()

Lib/test/test_extcall.py

@@ -52,15 +52,15 @@ Here we add keyword arguments
     >>> f(1, 2, **{'a': -1, 'b': 5}, **{'a': 4, 'c': 6})
     Traceback (most recent call last):
         ...
-    TypeError: f() got multiple values for keyword argument 'a'
+    TypeError: test.test_extcall.f() got multiple values for keyword argument 'a'
     >>> f(1, 2, **{'a': -1, 'b': 5}, a=4, c=6)
     Traceback (most recent call last):
         ...
-    TypeError: f() got multiple values for keyword argument 'a'
+    TypeError: test.test_extcall.f() got multiple values for keyword argument 'a'
     >>> f(1, 2, a=3, **{'a': 4}, **{'a': 5})
     Traceback (most recent call last):
         ...
-    TypeError: f() got multiple values for keyword argument 'a'
+    TypeError: test.test_extcall.f() got multiple values for keyword argument 'a'
     >>> f(1, 2, 3, *[4, 5], **{'a':6, 'b':7})
     (1, 2, 3, 4, 5) {'a': 6, 'b': 7}
     >>> f(1, 2, 3, x=4, y=5, *(6, 7), **{'a':8, 'b': 9})
@@ -118,7 +118,7 @@ Verify clearing of SF bug #733667
     >>> g(*Nothing())
     Traceback (most recent call last):
       ...
-    TypeError: g() argument after * must be an iterable, not Nothing
+    TypeError: test.test_extcall.g() argument after * must be an iterable, not Nothing
 
     >>> class Nothing:
     ...     def __len__(self): return 5
@@ -127,7 +127,7 @@ Verify clearing of SF bug #733667
     >>> g(*Nothing())
     Traceback (most recent call last):
       ...
-    TypeError: g() argument after * must be an iterable, not Nothing
+    TypeError: test.test_extcall.g() argument after * must be an iterable, not Nothing
 
     >>> class Nothing():
     ...     def __len__(self): return 5
@@ -247,17 +247,17 @@ What about willful misconduct?
     >>> h(*h)
     Traceback (most recent call last):
       ...
-    TypeError: h() argument after * must be an iterable, not function
+    TypeError: test.test_extcall.h() argument after * must be an iterable, not function
 
     >>> h(1, *h)
     Traceback (most recent call last):
       ...
-    TypeError: h() argument after * must be an iterable, not function
+    TypeError: test.test_extcall.h() argument after * must be an iterable, not function
 
     >>> h(*[1], *h)
     Traceback (most recent call last):
       ...
-    TypeError: h() argument after * must be an iterable, not function
+    TypeError: test.test_extcall.h() argument after * must be an iterable, not function
 
     >>> dir(*h)
     Traceback (most recent call last):
@@ -268,38 +268,38 @@ What about willful misconduct?
     >>> nothing(*h)
     Traceback (most recent call last):
       ...
-    TypeError: NoneType object argument after * must be an iterable, \
+    TypeError: None argument after * must be an iterable, \
 not function
 
     >>> h(**h)
     Traceback (most recent call last):
       ...
-    TypeError: h() argument after ** must be a mapping, not function
+    TypeError: test.test_extcall.h() argument after ** must be a mapping, not function
 
     >>> h(**[])
     Traceback (most recent call last):
       ...
-    TypeError: h() argument after ** must be a mapping, not list
+    TypeError: test.test_extcall.h() argument after ** must be a mapping, not list
 
     >>> h(a=1, **h)
     Traceback (most recent call last):
       ...
-    TypeError: h() argument after ** must be a mapping, not function
+    TypeError: test.test_extcall.h() argument after ** must be a mapping, not function
 
     >>> h(a=1, **[])
     Traceback (most recent call last):
       ...
-    TypeError: h() argument after ** must be a mapping, not list
+    TypeError: test.test_extcall.h() argument after ** must be a mapping, not list
 
     >>> h(**{'a': 1}, **h)
     Traceback (most recent call last):
       ...
-    TypeError: h() argument after ** must be a mapping, not function
+    TypeError: test.test_extcall.h() argument after ** must be a mapping, not function
 
     >>> h(**{'a': 1}, **[])
     Traceback (most recent call last):
       ...
-    TypeError: h() argument after ** must be a mapping, not list
+    TypeError: test.test_extcall.h() argument after ** must be a mapping, not list
 
     >>> dir(**h)
     Traceback (most recent call last):
@@ -309,7 +309,7 @@ not function
     >>> nothing(**h)
     Traceback (most recent call last):
       ...
-    TypeError: NoneType object argument after ** must be a mapping, \
+    TypeError: None argument after ** must be a mapping, \
 not function
 
     >>> dir(b=1, **{'b': 1})
@@ -351,17 +351,17 @@ Test a kwargs mapping with duplicated keys.
     >>> g(**MultiDict([('x', 1), ('x', 2)]))
     Traceback (most recent call last):
       ...
-    TypeError: g() got multiple values for keyword argument 'x'
+    TypeError: test.test_extcall.g() got multiple values for keyword argument 'x'
 
     >>> g(a=3, **MultiDict([('x', 1), ('x', 2)]))
     Traceback (most recent call last):
       ...
-    TypeError: g() got multiple values for keyword argument 'x'
+    TypeError: test.test_extcall.g() got multiple values for keyword argument 'x'
 
     >>> g(**MultiDict([('a', 3)]), **MultiDict([('x', 1), ('x', 2)]))
     Traceback (most recent call last):
       ...
-    TypeError: g() got multiple values for keyword argument 'x'
+    TypeError: test.test_extcall.g() got multiple values for keyword argument 'x'
 
 Another helper function
 

Lib/test/test_unpack_ex.py

@@ -236,27 +236,27 @@ Overridden parameters
     >>> f(x=5, **{'x': 3}, y=2)
     Traceback (most recent call last):
       ...
-    TypeError: f() got multiple values for keyword argument 'x'
+    TypeError: test.test_unpack_ex.f() got multiple values for keyword argument 'x'
 
     >>> f(**{'x': 3}, x=5, y=2)
     Traceback (most recent call last):
       ...
-    TypeError: f() got multiple values for keyword argument 'x'
+    TypeError: test.test_unpack_ex.f() got multiple values for keyword argument 'x'
 
     >>> f(**{'x': 3}, **{'x': 5}, y=2)
     Traceback (most recent call last):
       ...
-    TypeError: f() got multiple values for keyword argument 'x'
+    TypeError: test.test_unpack_ex.f() got multiple values for keyword argument 'x'
 
     >>> f(x=5, **{'x': 3}, **{'x': 2})
     Traceback (most recent call last):
       ...
-    TypeError: f() got multiple values for keyword argument 'x'
+    TypeError: test.test_unpack_ex.f() got multiple values for keyword argument 'x'
 
     >>> f(**{1: 3}, **{1: 5})
     Traceback (most recent call last):
       ...
-    TypeError: f() got multiple values for keyword argument '1'
+    TypeError: test.test_unpack_ex.f() got multiple values for keyword argument '1'
 
 Unpacking non-sequence
 

Misc/NEWS.d/next/C API/2019-07-21-21-08-47.bpo-37645.4DcUaI.rst

@@ -0,0 +1,2 @@
+Add :c:func:`_PyObject_FunctionStr` to get a user-friendly string representation
+of a function-like object. Patch by Jeroen Demeyer.

Objects/descrobject.c

@@ -231,45 +231,38 @@ getset_set(PyGetSetDescrObject *descr, PyObject *obj, PyObject *value)
  *
  * First, common helpers
  */
-static const char *
-get_name(PyObject *func) {
-    assert(PyObject_TypeCheck(func, &PyMethodDescr_Type));
-    return ((PyMethodDescrObject *)func)->d_method->ml_name;
-}
-
-typedef void (*funcptr)(void);
-
 static inline int
 method_check_args(PyObject *func, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
     assert(!PyErr_Occurred());
-    assert(PyObject_TypeCheck(func, &PyMethodDescr_Type));
     if (nargs < 1) {
-        PyErr_Format(PyExc_TypeError,
-                     "descriptor '%.200s' of '%.100s' "
-                     "object needs an argument",
-                     get_name(func), PyDescr_TYPE(func)->tp_name);
+        PyObject *funcstr = _PyObject_FunctionStr(func);
+        if (funcstr != NULL) {
+            PyErr_Format(PyExc_TypeError,
+                         "unbound method %U needs an argument", funcstr);
+            Py_DECREF(funcstr);
+        }
         return -1;
     }
     PyObject *self = args[0];
-    if (!_PyObject_RealIsSubclass((PyObject *)Py_TYPE(self),
-                                  (PyObject *)PyDescr_TYPE(func)))
-    {
-        PyErr_Format(PyExc_TypeError,
-                     "descriptor '%.200s' for '%.100s' objects "
-                     "doesn't apply to a '%.100s' object",
-                     get_name(func), PyDescr_TYPE(func)->tp_name,
-                     Py_TYPE(self)->tp_name);
+    PyObject *dummy;
+    if (descr_check((PyDescrObject *)func, self, &dummy)) {
         return -1;
     }
     if (kwnames && PyTuple_GET_SIZE(kwnames)) {
-        PyErr_Format(PyExc_TypeError,
-                     "%.200s() takes no keyword arguments", get_name(func));
+        PyObject *funcstr = _PyObject_FunctionStr(func);
+        if (funcstr != NULL) {
+            PyErr_Format(PyExc_TypeError,
+                         "%U takes no keyword arguments", funcstr);
+            Py_DECREF(funcstr);
+        }
         return -1;
     }
     return 0;
 }
 
+typedef void (*funcptr)(void);
+
 static inline funcptr
 method_enter_call(PyThreadState *tstate, PyObject *func)
 {
@@ -387,8 +380,12 @@ method_vectorcall_NOARGS(
         return NULL;
     }
     if (nargs != 1) {
-        PyErr_Format(PyExc_TypeError,
-            "%.200s() takes no arguments (%zd given)", get_name(func), nargs-1);
+        PyObject *funcstr = _PyObject_FunctionStr(func);
+        if (funcstr != NULL) {
+            PyErr_Format(PyExc_TypeError,
+                "%U takes no arguments (%zd given)", funcstr, nargs-1);
+            Py_DECREF(funcstr);
+        }
         return NULL;
     }
     PyCFunction meth = (PyCFunction)method_enter_call(tstate, func);
@@ -410,9 +407,13 @@ method_vectorcall_O(
         return NULL;
     }
     if (nargs != 2) {
-        PyErr_Format(PyExc_TypeError,
-            "%.200s() takes exactly one argument (%zd given)",
-            get_name(func), nargs-1);
+        PyObject *funcstr = _PyObject_FunctionStr(func);
+        if (funcstr != NULL) {
+            PyErr_Format(PyExc_TypeError,
+                "%U takes exactly one argument (%zd given)",
+                funcstr, nargs-1);
+            Py_DECREF(funcstr);
+        }
         return NULL;
     }
     PyCFunction meth = (PyCFunction)method_enter_call(tstate, func);

Objects/methodobject.c

@@ -334,15 +334,6 @@ _PyCFunction_Fini(void)
  *
  * First, common helpers
  */
-static const char *
-get_name(PyObject *func)
-{
-    assert(PyCFunction_Check(func));
-    PyMethodDef *method = ((PyCFunctionObject *)func)->m_ml;
-    return method->ml_name;
-}
-
-typedef void (*funcptr)(void);
 
 static inline int
 cfunction_check_kwargs(PyThreadState *tstate, PyObject *func, PyObject *kwnames)
@@ -350,13 +341,19 @@ cfunction_check_kwargs(PyThreadState *tstate, PyObject *func, PyObject *kwnames)
     assert(!_PyErr_Occurred(tstate));
     assert(PyCFunction_Check(func));
     if (kwnames && PyTuple_GET_SIZE(kwnames)) {
-        _PyErr_Format(tstate, PyExc_TypeError,
-                      "%.200s() takes no keyword arguments", get_name(func));
+        PyObject *funcstr = _PyObject_FunctionStr(func);
+        if (funcstr != NULL) {
+            _PyErr_Format(tstate, PyExc_TypeError,
+                         "%U takes no keyword arguments", funcstr);
+            Py_DECREF(funcstr);
+        }
         return -1;
     }
     return 0;
 }
 
+typedef void (*funcptr)(void);
+
 static inline funcptr
 cfunction_enter_call(PyThreadState *tstate, PyObject *func)
 {
@@ -412,9 +409,12 @@ cfunction_vectorcall_NOARGS(
     }
     Py_ssize_t nargs = PyVectorcall_NARGS(nargsf);
     if (nargs != 0) {
-        _PyErr_Format(tstate, PyExc_TypeError,
-                      "%.200s() takes no arguments (%zd given)",
-                      get_name(func), nargs);
+        PyObject *funcstr = _PyObject_FunctionStr(func);
+        if (funcstr != NULL) {
+            _PyErr_Format(tstate, PyExc_TypeError,
+                "%U takes no arguments (%zd given)", funcstr, nargs);
+            Py_DECREF(funcstr);
+        }
         return NULL;
     }
     PyCFunction meth = (PyCFunction)cfunction_enter_call(tstate, func);
@@ -436,9 +436,12 @@ cfunction_vectorcall_O(
     }
     Py_ssize_t nargs = PyVectorcall_NARGS(nargsf);
     if (nargs != 1) {
-        _PyErr_Format(tstate, PyExc_TypeError,
-                      "%.200s() takes exactly one argument (%zd given)",
-                      get_name(func), nargs);
+        PyObject *funcstr = _PyObject_FunctionStr(func);
+        if (funcstr != NULL) {
+            _PyErr_Format(tstate, PyExc_TypeError,
+                "%U takes exactly one argument (%zd given)", funcstr, nargs);
+            Py_DECREF(funcstr);
+        }
         return NULL;
     }
     PyCFunction meth = (PyCFunction)cfunction_enter_call(tstate, func);

Objects/object.c

@@ -681,6 +681,64 @@ PyObject_Bytes(PyObject *v)
     return PyBytes_FromObject(v);
 }
 
+
+/*
+def _PyObject_FunctionStr(x):
+    try:
+        qualname = x.__qualname__
+    except AttributeError:
+        return str(x)
+    try:
+        mod = x.__module__
+        if mod is not None and mod != 'builtins':
+            return f"{x.__module__}.{qualname}()"
+    except AttributeError:
+        pass
+    return qualname
+*/
+PyObject *
+_PyObject_FunctionStr(PyObject *x)
+{
+    _Py_IDENTIFIER(__module__);
+    _Py_IDENTIFIER(__qualname__);
+    _Py_IDENTIFIER(builtins);
+    assert(!PyErr_Occurred());
+    PyObject *qualname;
+    int ret = _PyObject_LookupAttrId(x, &PyId___qualname__, &qualname);
+    if (qualname == NULL) {
+        if (ret < 0) {
+            return NULL;
+        }
+        return PyObject_Str(x);
+    }
+    PyObject *module;
+    PyObject *result = NULL;
+    ret = _PyObject_LookupAttrId(x, &PyId___module__, &module);
+    if (module != NULL && module != Py_None) {
+        PyObject *builtinsname = _PyUnicode_FromId(&PyId_builtins);
+        if (builtinsname == NULL) {
+            goto done;
+        }
+        ret = PyObject_RichCompareBool(module, builtinsname, Py_NE);
+        if (ret < 0) {
+            // error
+            goto done;
+        }
+        if (ret > 0) {
+            result = PyUnicode_FromFormat("%S.%S()", module, qualname);
+            goto done;
+        }
+    }
+    else if (ret < 0) {
+        goto done;
+    }
+    result = PyUnicode_FromFormat("%S()", qualname);
+done:
+    Py_DECREF(qualname);
+    Py_XDECREF(module);
+    return result;
+}
+
 /* For Python 3.0.1 and later, the old three-way comparison has been
    completely removed in favour of rich comparisons.  PyObject_Compare() and
    PyObject_Cmp() are gone, and the builtin cmp function no longer exists.

Python/ceval.c

@@ -5351,12 +5351,17 @@ static int
 check_args_iterable(PyThreadState *tstate, PyObject *func, PyObject *args)
 {
     if (args->ob_type->tp_iter == NULL && !PySequence_Check(args)) {
-        _PyErr_Format(tstate, PyExc_TypeError,
-                      "%.200s%.200s argument after * "
-                      "must be an iterable, not %.200s",
-                      PyEval_GetFuncName(func),
-                      PyEval_GetFuncDesc(func),
-                      args->ob_type->tp_name);
+        /* check_args_iterable() may be called with a live exception:
+         * clear it to prevent calling _PyObject_FunctionStr() with an
+         * exception set. */
+        PyErr_Clear();
+        PyObject *funcstr = _PyObject_FunctionStr(func);
+        if (funcstr != NULL) {
+            _PyErr_Format(tstate, PyExc_TypeError,
+                          "%U argument after * must be an iterable, not %.200s",
+                          funcstr, Py_TYPE(args)->tp_name);
+            Py_DECREF(funcstr);
+        }
         return -1;
     }
     return 0;
@@ -5372,24 +5377,30 @@ format_kwargs_error(PyThreadState *tstate, PyObject *func, PyObject *kwargs)
      * is not a mapping.
      */
     if (_PyErr_ExceptionMatches(tstate, PyExc_AttributeError)) {
-        _PyErr_Format(tstate, PyExc_TypeError,
-                      "%.200s%.200s argument after ** "
-                      "must be a mapping, not %.200s",
-                      PyEval_GetFuncName(func),
-                      PyEval_GetFuncDesc(func),
-                      kwargs->ob_type->tp_name);
+        PyErr_Clear();
+        PyObject *funcstr = _PyObject_FunctionStr(func);
+        if (funcstr != NULL) {
+            _PyErr_Format(
+                tstate, PyExc_TypeError,
+                "%U argument after ** must be a mapping, not %.200s",
+                funcstr, Py_TYPE(kwargs)->tp_name);
+            Py_DECREF(funcstr);
+        }
     }
     else if (_PyErr_ExceptionMatches(tstate, PyExc_KeyError)) {
         PyObject *exc, *val, *tb;
         _PyErr_Fetch(tstate, &exc, &val, &tb);
         if (val && PyTuple_Check(val) && PyTuple_GET_SIZE(val) == 1) {
-            PyObject *key = PyTuple_GET_ITEM(val, 0);
-            _PyErr_Format(tstate, PyExc_TypeError,
-                          "%.200s%.200s got multiple "
-                          "values for keyword argument '%S'",
-                          PyEval_GetFuncName(func),
-                          PyEval_GetFuncDesc(func),
-                          key);
+            PyErr_Clear();
+            PyObject *funcstr = _PyObject_FunctionStr(func);
+            if (funcstr != NULL) {
+                PyObject *key = PyTuple_GET_ITEM(val, 0);
+                _PyErr_Format(
+                    tstate, PyExc_TypeError,
+                    "%U got multiple values for keyword argument '%S'",
+                    funcstr, key);
+                Py_DECREF(funcstr);
+            }
             Py_XDECREF(exc);
             Py_XDECREF(val);
             Py_XDECREF(tb);