PyAPI: add BPY_execute_string_as_string

Utility to execute a string and get the resulting string,
matching BPY_execute_string_as_number.

Not used just yet but generally useful function.

source/blender/python/BPY_extern.h

@@ -76,6 +76,7 @@ void BPY_thread_restore(BPy_ThreadStatePtr tstate);
 bool	BPY_execute_filepath(struct bContext *C, const char *filepath, struct ReportList *reports);
 bool	BPY_execute_text(struct bContext *C, struct Text *text, struct ReportList *reports, const bool do_jump);
 bool	BPY_execute_string_as_number(struct bContext *C, const char *expr, const bool verbose, double *r_value);
+bool	BPY_execute_string_as_string(struct bContext *C, const char *expr, const bool verbose, char **r_value);
 bool	BPY_execute_string_ex(struct bContext *C, const char *expr, bool use_eval);
 bool	BPY_execute_string(struct bContext *C, const char *expr);
 

source/blender/python/generic/py_capi_utils.c

@@ -1070,4 +1070,41 @@ bool PyC_RunString_AsNumber(const char *expr, const char *filename, double *r_va
 	return ok;
 }
 
+bool PyC_RunString_AsString(const char *expr, const char *filename, char **r_value)
+{
+	PyObject *py_dict, *retval;
+	bool ok = true;
+	PyObject *main_mod = NULL;
+
+	PyC_MainModule_Backup(&main_mod);
+
+	py_dict = PyC_DefaultNameSpace(filename);
+
+	retval = PyRun_String(expr, Py_eval_input, py_dict, py_dict);
+
+	if (retval == NULL) {
+		ok = false;
+	}
+	else {
+		const char *val;
+		Py_ssize_t val_len;
+
+		val = _PyUnicode_AsStringAndSize(retval, &val_len);
+		if (val == NULL && PyErr_Occurred()) {
+			ok = false;
+		}
+		else {
+			char *val_alloc = MEM_mallocN(val_len + 1, __func__);
+			memcpy(val_alloc, val, val_len + 1);
+			*r_value = val_alloc;
+		}
+
+		Py_DECREF(retval);
+	}
+
+	PyC_MainModule_Restore(main_mod);
+
+	return ok;
+}
+
 #endif  /* #ifndef MATH_STANDALONE */

source/blender/python/generic/py_capi_utils.h

@@ -81,6 +81,7 @@ int       PyC_FlagSet_ToBitfield(PyC_FlagSet *items, PyObject *value, int *r_val
 PyObject *PyC_FlagSet_FromBitfield(PyC_FlagSet *items, int flag);
 
 bool PyC_RunString_AsNumber(const char *expr, const char *filename, double *r_value);
+bool PyC_RunString_AsString(const char *expr, const char *filename, char **r_value);
 
 int PyC_ParseBool(PyObject *o, void *p);
 

source/blender/python/intern/bpy_interface.c

@@ -604,6 +604,42 @@ bool BPY_execute_string_as_number(bContext *C, const char *expr, const bool verb
 	return ok;
 }
 
+/**
+ * \return success
+ */
+bool BPY_execute_string_as_string(bContext *C, const char *expr, const bool verbose, char **r_value)
+{
+	PyGILState_STATE gilstate;
+	bool ok = true;
+
+	if (!r_value || !expr) {
+		return -1;
+	}
+
+	if (expr[0] == '\0') {
+		*r_value = NULL;
+		return ok;
+	}
+
+	bpy_context_set(C, &gilstate);
+
+	ok = PyC_RunString_AsString(expr, "<blender button>", r_value);
+
+	if (ok == false) {
+		if (verbose) {
+			BPy_errors_to_report_ex(CTX_wm_reports(C), false, false);
+		}
+		else {
+			PyErr_Clear();
+		}
+	}
+
+	bpy_context_clear(C, &gilstate);
+
+	return ok;
+}
+
+
 bool BPY_execute_string_ex(bContext *C, const char *expr, bool use_eval)
 {
 	PyGILState_STATE gilstate;