[ python-Bugs-966618 ] float_subtype_new() bug

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Bugs item #966618, was opened at 2004-06-04 15:39
Message generated for change (Comment added) made by nascheme
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Category: Python Interpreter Core
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Armin Rigo (arigo)
Assigned to: Nobody/Anonymous (nobody)
Summary: float_subtype_new() bug

Initial Comment:
A rather obsure bug in the subclassing code:

>>> class A:
...   def __float__(self): return 'hello'
...
>>> float(A())
'hello'

>>> class f(float): pass
...
>>> f(A())
-5.7590155905901735e-56

In debug mode, the assert() in float_subtype_new() fails instead.  In non-debug mode, the value we get is the result of typecasting the PyStringObject* to a PyFloatObject*.

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>Comment By: Neil Schemenauer (nascheme)
Date: 2004-06-05 19:46

Message:
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I think the right fix is to have PyNumber_Int,
PyNumber_Float, and PyNumber_Long check the return value of
slot function (i.e. nb_int, nb_float).  That matches the
behavior of PyObject_Str and PyObject_Repr.

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Comment By: Aaron Brady (insomnike)
Date: 2004-06-05 13:13

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(ack, spelling error copied from intobject.c)

###
--- floatobject.c-      Sat Jun  5 13:21:07 2004
+++ floatobject.c       Sat Jun  5 13:23:00 2004
@@ -765,7 +765,13 @@
        tmp = float_new(&PyFloat_Type, args, kwds);
        if (tmp == NULL)
                return NULL;
-       assert(PyFloat_CheckExact(tmp));
+       if(!PyFloat_CheckExact(tmp)) {
+               PyErr_SetString(PyExc_ValueError,
+                               "value must be convertable
to a float");
+               Py_DECREF(tmp);
+               return NULL;
+       }
+
        new = type->tp_alloc(type, 0);
        if (new == NULL) {
                Py_DECREF(tmp);
###

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Comment By: Aaron Brady (insomnike)
Date: 2004-06-05 13:11

Message:
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(Inline, I can't seem to attach things)

###
--- floatobject.c-      Sat Jun  5 13:21:07 2004
+++ floatobject.c       Sat Jun  5 13:23:00 2004
@@ -765,7 +765,13 @@
        tmp = float_new(&PyFloat_Type, args, kwds);
        if (tmp == NULL)
                return NULL;
-       assert(PyFloat_CheckExact(tmp));
+       if(!PyFloat_CheckExact(tmp)) {
+               PyErr_SetString(PyExc_ValueError,
+                               "value must convertable to a
float");
+               Py_DECREF(tmp);
+               return NULL;
+       }
+
        new = type->tp_alloc(type, 0);
        if (new == NULL) {
                Py_DECREF(tmp);
###

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Comment By: Aaron Brady (insomnike)
Date: 2004-06-05 13:01

Message:
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user_id=1057404

floatobject.c contains an assertion that the value can be
coerced into a float, but not a runtime if. I've changed it
to be in line with what int_subtype_new() does.

This may not be 100% correct, however, as they both allow a
string to be returned from __int__() and __float__(),
respectively. complex() does not allow this, however, and it
throws TypeError (while int_subtype_new() and
float_subtype_new() throw ValueError).

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