bind: WIP add checks for exception being set in wrapped python functions

This commit starts to address the issue of a non-NULL PyObject* being returned when an exception has been set by the wrapped C function. Adds a checking mechanism for PyErr_Occurred. Results in exceptions being propagated to python caller, but may introduce memory leaks for retval not being cleaned up during error.

Refs go-python/gopy #254

_examples/pyerrors/pyerrors.go

@@ -5,7 +5,10 @@
 // Package pyerrors holds functions returning an error.
 package pyerrors
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+)
 
 // Div is a function for detecting errors.
 func Div(i, j int) (int, error) {
@@ -14,3 +17,18 @@ func Div(i, j int) (int, error) {
 	}
 	return i / j, nil
 }
+
+type Stringer fmt.Stringer
+type MyString string
+
+func (t MyString) String() string { return string(t) }
+
+// NewMyString converts a string to a custom MyString type.
+// It is an error to pass an empty string value.
+func NewMyString(val string) (stringer Stringer, err error) {
+	if val == "" {
+		err = errors.New("Empty string value.")
+		return
+	}
+	return MyString(val), nil
+}

_examples/pyerrors/test.py

@@ -14,7 +14,19 @@ def div(a, b):
     except Exception as e:
         print(e)
 
-div(5,0)
+
+def new_mystring(s):
+    try:
+        ms = pyerrors.NewMyString(s)
+        print('pyerrors.NewMyString("%s") = "%s"'% (s, ms.String()))
+    except Exception as e:
+        print(e)
+
+
+div(5,0)  # error
 div(5,2)
 
+new_mystring("")  # error
+new_mystring("hello")
+
 print("OK")

bind/gen.go

@@ -203,9 +203,30 @@ func GoPyMainRun() {
 # File is generated by gopy. Do not edit.
 # %[2]s
 
-from pybindgen import retval, param, Module
+from pybindgen import retval, param, Function, Module
 import sys
 
+class CheckedFunction(Function):
+    def __init__(self, *a, **kw):
+        super(CheckedFunction, self).__init__(*a, **kw)
+        self._failure_expression = kw.get('failure_expression', '')
+
+    def set_failure_expression(self, expr):
+        self._failure_expression = expr
+
+    def generate_call(self):
+        super(CheckedFunction, self).generate_call()
+        check = "PyErr_Occurred()"
+        if self._failure_expression:
+            check = "{} && {}".format(self._failure_expression, check)
+        self.before_call.write_error_check(check)
+
+def add_checked_function(mod, name, retval, params, failure_expression='', *a, **kw):
+    fn = CheckedFunction(name, retval, params, *a, **kw)
+    fn.set_failure_expression(failure_expression)
+    mod._add_function_obj(fn)
+    return fn
+
 mod = Module('_%[1]s')
 mod.add_include('"%[1]s_go.h"')
 mod.add_function('GoPyInit', None, [])

bind/gen_func.go

@@ -156,14 +156,14 @@ func (g *pyGen) genFuncSig(sym *symbol, fsym *Func) bool {
 		g.gofile.Printf("\n//export %s\n", mnm)
 		g.gofile.Printf("func %s(", mnm)
 
-		g.pybuild.Printf("mod.add_function('%s', ", mnm)
+		g.pybuild.Printf("add_checked_function(mod, '%s', ", mnm)
 
 		g.pywrap.Printf("def %s(", gname)
 	default:
 		g.gofile.Printf("\n//export %s\n", fsym.ID())
 		g.gofile.Printf("func %s(", fsym.ID())
 
-		g.pybuild.Printf("mod.add_function('%s', ", fsym.ID())
+		g.pybuild.Printf("add_checked_function(mod, '%s', ", fsym.ID())
 
 		g.pywrap.Printf("def %s(", gname)
 	}

main_test.go

@@ -181,7 +181,7 @@ Add(int i, int j) int
 --- hi.LookupQuestion(42)...
 Life, the Universe and Everything
 --- hi.LookupQuestion(12)...
-caught: <built-in function hi_LookupQuestion> returned a result with an error set
+caught: Wrong answer: 12 != 42
 --- doc(hi.Person):
 Person is a simple struct
 
@@ -209,9 +209,9 @@ hi.Person{Name="foo", Age=42}
 --- p.Name: foo
 --- p.Work(2)...
 --- p.Work(24)...
-caught: <built-in function hi_Person_Work> returned a result with an error set
+caught: can't work for 24 hours!
 --- p.Salary(2): 20
---- p.Salary(24): caught: <built-in function hi_Person_Salary> returned a result with an error set
+--- p.Salary(24): caught: can't work for 24 hours!
 --- Person.__init__
 caught: argument 2 must be str, not int | err-type: <class 'TypeError'>
 caught: an integer is required (got type str) | err-type: <class 'TypeError'>
@@ -545,11 +545,13 @@ func TestPyErrors(t *testing.T) {
 	path := "_examples/pyerrors"
 	testPkg(t, pkg{
 		path:   path,
-		lang:   features[path], // TODO: should print out the error message!
+		lang:   features[path],
 		cmd:    "build",
 		extras: nil,
-		want: []byte(`<built-in function pyerrors_Div> returned a result with an error set
+		want: []byte(`Divide by zero.
 pyerrors.Div(5, 2) = 2
+Empty string value.
+pyerrors.NewMyString("hello") = "hello"
 OK
 `),
 	})