From a15dece51975ddc94b488a64c1326d3e39566c59 Mon Sep 17 00:00:00 2001
From: Guido van Rossum <guido@python.org>
Date: Fri, 24 Aug 2001 18:48:27 +0000
Subject: Improve the error message issued when an unbound method is called
 with an inappropriate first argument.  Now that there are more ways for this
 to fail, make sure to report the name of the class of the expected instance
 and of the actual instance.

---
 Objects/classobject.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 49 insertions(+), 3 deletions(-)

diff --git a/Objects/classobject.c b/Objects/classobject.c
index f1145a4..f3f7e69 100644
--- a/Objects/classobject.c
+++ b/Objects/classobject.c
@@ -2127,6 +2127,48 @@ instancemethod_traverse(PyMethodObject *im, visitproc visit, void *arg)
 	return 0;
 }
 
+static char *
+getclassname(PyObject *class)
+{
+	PyObject *name;
+
+	if (class == NULL)
+		name = NULL;
+	else
+		name = PyObject_GetAttrString(class, "__name__");
+	if (name == NULL) {
+		PyErr_Clear();
+		return "?";
+	}
+	if (!PyString_Check(name)) {
+		Py_DECREF(name);
+		return "?";
+	}
+	PyString_InternInPlace(&name);
+	Py_DECREF(name);
+	return PyString_AS_STRING(name);
+}
+
+static char *
+getinstclassname(PyObject *inst)
+{
+	PyObject *class;
+	char *name;
+
+	if (inst == NULL)
+		return "nothing";
+
+	class = PyObject_GetAttrString(inst, "__class__");
+	if (class == NULL) {
+		PyErr_Clear();
+		class = (PyObject *)(inst->ob_type);
+		Py_INCREF(class);
+	}
+	name = getclassname(class);
+	Py_XDECREF(class);
+	return name;
+}
+
 static PyObject *
 instancemethod_call(PyObject *func, PyObject *arg, PyObject *kw)
 {
@@ -2150,10 +2192,14 @@ instancemethod_call(PyObject *func, PyObject *arg, PyObject *kw)
 		}
 		if (!ok) {
 			PyErr_Format(PyExc_TypeError,
-				     "unbound method %s%s must be "
-				     "called with instance as first argument",
+				     "unbound method %s%s must be called with "
+				     "%s instance as first argument "
+				     "(got %s%s instead)",
 				     PyEval_GetFuncName(func),
-				     PyEval_GetFuncDesc(func));
+				     PyEval_GetFuncDesc(func),
+				     getclassname(class),
+				     getinstclassname(self),
+				     self == NULL ? "" : " instance");
 			return NULL;
 		}
 		Py_INCREF(arg);
-- 
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