Fix uses of PyObject_IsTrue.

anntzer · anntzer · commit 93eaf6df9534 · 2019-06-08T12:37:35.000+02:00
PyObject_IsTrue can return -1 if an exception occurred when trying to
convert a Python object to a bool (a typical case is for numpy arrays,
which cannot be converted to bools).  Failure to handle this correctly
results e.g. in
```
l, = plt.plot([1, 2]); l.get_path().should_simplify = np.array([1, 2])
```
```
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/lib/python3.7/site-packages/matplotlib/backends/backend_qt5.py", line 501, in _draw_idle
&lt;elided&gt;
  File "/usr/lib/python3.7/site-packages/matplotlib/backends/backend_agg.py", line 146, in draw_path
    self._renderer.draw_path(gc, path, transform, rgbFace)
SystemError: PyEval_EvalFrameEx returned a result with an error set
```
whereas after this PR, the ValueError gets correctly propagated out.

No tests, because one really needs to go out of their way to trigger the
faulty cases anyways...
diff --git a/src/_path_wrapper.cpp b/src/_path_wrapper.cpp
@@ -631,8 +631,12 @@ static PyObject *Py_cleanup_path(PyObject *self, PyObject *args, PyObject *kwds)
 
     if (simplifyobj == Py_None) {
         simplify = path.should_simplify();
-    } else if (PyObject_IsTrue(simplifyobj)) {
-        simplify = true;
+    } else {
+        switch (PyObject_IsTrue(simplifyobj)) {
+            case 0: simplify = false; break;
+            case 1: simplify = true; break;
+            default: return NULL;  // errored.
+        }
     }
 
     bool do_clip = (clip_rect.x1 < clip_rect.x2 && clip_rect.y1 < clip_rect.y2);
@@ -709,8 +713,12 @@ static PyObject *Py_convert_to_string(PyObject *self, PyObject *args, PyObject *
 
     if (simplifyobj == Py_None) {
         simplify = path.should_simplify();
-    } else if (PyObject_IsTrue(simplifyobj)) {
-        simplify = true;
+    } else {
+        switch (PyObject_IsTrue(simplifyobj)) {
+            case 0: simplify = false; break;
+            case 1: simplify = true; break;
+            default: return NULL;  // errored.
+        }
     }
 
     CALL_CPP("convert_to_string",
diff --git a/src/py_converters.cpp b/src/py_converters.cpp
@@ -116,14 +116,11 @@ int convert_double(PyObject *obj, void *p)
 int convert_bool(PyObject *obj, void *p)
 {
     bool *val = (bool *)p;
-    int ret;
-
-    ret = PyObject_IsTrue(obj);
-    if (ret == -1) {
-        return 0;
+    switch (PyObject_IsTrue(obj)) {
+        case 0: *val = false; break;
+        case 1: *val = true; break;
+        default: return 0;  // errored.
     }
-    *val = ret != 0;
-
     return 1;
 }
 
@@ -389,7 +386,11 @@ int convert_path(PyObject *obj, void *pathp)
     if (should_simplify_obj == NULL) {
         goto exit;
     }
-    should_simplify = PyObject_IsTrue(should_simplify_obj) != 0;
+    switch (PyObject_IsTrue(should_simplify_obj)) {
+        case 0: should_simplify = 0; break;
+        case 1: should_simplify = 1; break;
+        default: goto exit;  // errored.
+    }
 
     simplify_threshold_obj = PyObject_GetAttrString(obj, "simplify_threshold");
     if (simplify_threshold_obj == NULL) {
@@ -438,15 +439,15 @@ int convert_clippath(PyObject *clippath_tuple, void *clippathp)
 int convert_snap(PyObject *obj, void *snapp)
 {
     e_snap_mode *snap = (e_snap_mode *)snapp;
-
     if (obj == NULL || obj == Py_None) {
         *snap = SNAP_AUTO;
-    } else if (PyObject_IsTrue(obj)) {
-        *snap = SNAP_TRUE;
     } else {
-        *snap = SNAP_FALSE;
+        switch (PyObject_IsTrue(obj)) {
+            case 0: *snap = SNAP_FALSE; break;
+            case 1: *snap = SNAP_TRUE; break;
+            default: return 0;  // errored.
+        }
     }
-
     return 1;
 }
 
