New submission from Alexey Izbyshev <[email protected]>:
range_repr() contains the following snippet:
/* Check for special case values for printing. We don't always
need the step value. We don't care about errors
(it means overflow), so clear the errors. */
istep = PyNumber_AsSsize_t(r->step, NULL);
if (istep != 1 || (istep == -1 && PyErr_Occurred())) {
PyErr_Clear();
}
The second condition in 'if' statement is always false (reported by Svace
static analyzer). Moreover, the comment is incorrect. It implies that any error
from PyNumber_AsSsize_t() means that an overflow occurred, but according to its
implementation and documentation, any error is guaranteed *not* to be an
OverflowError if the second parameter is NULL (the result is clamped on
overflow).
In practice, 'range' invariants currently guarantee that no error can occur in
this case because 'r->step' is a subtype of int (enforced in validate_step()).
So the 'if' statement can be replaced either with an assert:
assert(!(istep == -1 && PyErr_Occurred()))
or with a conservative check:
if (istep == -1 && PyErr_Occurred())) {
// may also add assert(!PyErr_ExceptionMatches( PyExc_OverflowError);
return NULL;
}
Suggestions are appreciated.
----------
components: Interpreter Core
messages: 323912
nosy: izbyshev, ncoghlan, serhiy.storchaka
priority: normal
severity: normal
status: open
title: An always-false condition in range_repr() from Objects/rangeobject.c
type: behavior
versions: Python 3.6, Python 3.7, Python 3.8
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Python tracker <[email protected]>
<https://bugs.python.org/issue34468>
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