[libgpiod][PATCH v2] bindings: python: import gpiod attributes in external module

[Vincent Fazio <vfazio@xxxxxxxxxxx>]

Previously, the external module relied on gpiod attributes being present
within `globals()` to construct return values back to the caller.

This assumption required callers of the external module to have imported
the attributes to populate `globals()` for the interface to work.

Having this implicit contract is opaque and prone to causing issues if
imports within gpiod modules ever get reworked.

Now, the external module explicitly imports attributes from gpiod in
order to return values back to the caller.

There should be no concern about circular imports as the external module
should be completely imported by the time callers call into it.

Since Py_gpiod_GetGlobalType is no longer used, it has been replaced
with Py_gpiod_GetModuleAttrString which returns a new PyObject*
reference for the named module and attribute that must be decremented
when no longer in use.

Closes: https://github.com/brgl/libgpiod/issues/101
Signed-off-by: Vincent Fazio <vfazio@xxxxxxxxxxx>
---
Changes since v1:

* decrement attribute reference on successful returns from 
  request_get_values and request_read_edge_events (Thanks Bartosz)

---
 bindings/python/gpiod/ext/chip.c     | 39 +++++++++++++++++-----------
 bindings/python/gpiod/ext/common.c   | 14 ++++++----
 bindings/python/gpiod/ext/internal.h |  3 ++-
 bindings/python/gpiod/ext/request.c  | 28 +++++++++++++-------
 4 files changed, 54 insertions(+), 30 deletions(-)

diff --git a/bindings/python/gpiod/ext/chip.c b/bindings/python/gpiod/ext/chip.c
index e8eaad8..fcfb960 100644
--- a/bindings/python/gpiod/ext/chip.c
+++ b/bindings/python/gpiod/ext/chip.c
@@ -75,31 +75,34 @@ static PyObject *chip_get_info(chip_object *self, PyObject *Py_UNUSED(ignored))
 	struct gpiod_chip_info *info;
 	PyObject *type, *ret;
 
-	type = Py_gpiod_GetGlobalType("ChipInfo");
+	type = Py_gpiod_GetModuleAttrString("gpiod.chip_info", "ChipInfo");
 	if (!type)
 		return NULL;
 
 	info = gpiod_chip_get_info(self->chip);
-	if (!info)
+	if (!info) {
+		Py_DECREF(type);
 		return PyErr_SetFromErrno(PyExc_OSError);
+	}
 
-	 ret = PyObject_CallFunction(type, "ssI",
-				     gpiod_chip_info_get_name(info),
-				     gpiod_chip_info_get_label(info),
-				     gpiod_chip_info_get_num_lines(info));
-	 gpiod_chip_info_free(info);
-	 return ret;
+	ret = PyObject_CallFunction(type, "ssI",
+				    gpiod_chip_info_get_name(info),
+				    gpiod_chip_info_get_label(info),
+				    gpiod_chip_info_get_num_lines(info));
+	gpiod_chip_info_free(info);
+	Py_DECREF(type);
+	return ret;
 }
 
 static PyObject *make_line_info(struct gpiod_line_info *info)
 {
-	PyObject *type;
+	PyObject *type, *ret;
 
-	type = Py_gpiod_GetGlobalType("LineInfo");
+	type = Py_gpiod_GetModuleAttrString("gpiod.line_info", "LineInfo");
 	if (!type)
 		return NULL;
 
-	return PyObject_CallFunction(type, "IsOsiOiiiiOk",
+	ret = PyObject_CallFunction(type, "IsOsiOiiiiOk",
 				gpiod_line_info_get_offset(info),
 				gpiod_line_info_get_name(info),
 				gpiod_line_info_is_used(info) ?
@@ -115,6 +118,8 @@ static PyObject *make_line_info(struct gpiod_line_info *info)
 				gpiod_line_info_is_debounced(info) ?
 							Py_True : Py_False,
 				gpiod_line_info_get_debounce_period_us(info));
+	Py_DECREF(type);
+	return ret;
 }
 
 static PyObject *chip_get_line_info(chip_object *self, PyObject *args)
@@ -168,10 +173,6 @@ chip_read_info_event(chip_object *self, PyObject *Py_UNUSED(ignored))
 	struct gpiod_info_event *event;
 	struct gpiod_line_info *info;
 
-	type = Py_gpiod_GetGlobalType("InfoEvent");
-	if (!type)
-		return NULL;
-
 	Py_BEGIN_ALLOW_THREADS;
 	event = gpiod_chip_read_info_event(self->chip);
 	Py_END_ALLOW_THREADS;
@@ -186,12 +187,20 @@ chip_read_info_event(chip_object *self, PyObject *Py_UNUSED(ignored))
 		return NULL;
 	}
 
+	type = Py_gpiod_GetModuleAttrString("gpiod.info_event", "InfoEvent");
+	if (!type) {
+		Py_DECREF(info_obj);
+		gpiod_info_event_free(event);
+		return NULL;
+	}
+
 	event_obj = PyObject_CallFunction(type, "iKO",
 				gpiod_info_event_get_event_type(event),
 				gpiod_info_event_get_timestamp_ns(event),
 				info_obj);
 	Py_DECREF(info_obj);
 	gpiod_info_event_free(event);
+	Py_DECREF(type);
 	return event_obj;
 }
 
diff --git a/bindings/python/gpiod/ext/common.c b/bindings/python/gpiod/ext/common.c
index 07fca8c..62201b6 100644
--- a/bindings/python/gpiod/ext/common.c
+++ b/bindings/python/gpiod/ext/common.c
@@ -64,15 +64,19 @@ PyObject *Py_gpiod_SetErrFromErrno(void)
 	return PyErr_SetFromErrno(exc);
 }
 
-PyObject *Py_gpiod_GetGlobalType(const char *type_name)
+PyObject *Py_gpiod_GetModuleAttrString(const char *modname,
+				       const char *attrname)
 {
-	PyObject *globals;
+	PyObject *module, *attribute;
 
-	globals = PyEval_GetGlobals();
-	if (!globals)
+	module = PyImport_ImportModule(modname);
+	if (!module)
 		return NULL;
 
-	return PyDict_GetItemString(globals, type_name);
+	attribute = PyObject_GetAttrString(module, attrname);
+	Py_DECREF(module);
+
+	return attribute;
 }
 
 unsigned int Py_gpiod_PyLongAsUnsignedInt(PyObject *pylong)
diff --git a/bindings/python/gpiod/ext/internal.h b/bindings/python/gpiod/ext/internal.h
index 7d223c0..15aedfb 100644
--- a/bindings/python/gpiod/ext/internal.h
+++ b/bindings/python/gpiod/ext/internal.h
@@ -8,7 +8,8 @@
 #include <Python.h>
 
 PyObject *Py_gpiod_SetErrFromErrno(void);
-PyObject *Py_gpiod_GetGlobalType(const char *type_name);
+PyObject *Py_gpiod_GetModuleAttrString(const char *modname,
+				       const char *attrname);
 unsigned int Py_gpiod_PyLongAsUnsignedInt(PyObject *pylong);
 void Py_gpiod_dealloc(PyObject *self);
 PyObject *Py_gpiod_MakeRequestObject(struct gpiod_line_request *request,
diff --git a/bindings/python/gpiod/ext/request.c b/bindings/python/gpiod/ext/request.c
index 5db69fe..e1a2a42 100644
--- a/bindings/python/gpiod/ext/request.c
+++ b/bindings/python/gpiod/ext/request.c
@@ -149,10 +149,6 @@ static PyObject *request_get_values(request_object *self, PyObject *args)
 	if (num_offsets < 0)
 		return NULL;
 
-	type = Py_gpiod_GetGlobalType("Value");
-	if (!type)
-		return NULL;
-
 	iter = PyObject_GetIter(offsets);
 	if (!iter)
 		return NULL;
@@ -183,18 +179,26 @@ static PyObject *request_get_values(request_object *self, PyObject *args)
 	if (ret)
 		return Py_gpiod_SetErrFromErrno();
 
+	type = Py_gpiod_GetModuleAttrString("gpiod.line", "Value");
+	if (!type)
+		return NULL;
+
 	for (pos = 0; pos < num_offsets; pos++) {
 		val = PyObject_CallFunction(type, "i", self->values[pos]);
-		if (!val)
+		if (!val) {
+			Py_DECREF(type);
 			return NULL;
+		}
 
 		ret = PyList_SetItem(values, pos, val);
 		if (ret) {
 			Py_DECREF(val);
+			Py_DECREF(type);
 			return NULL;
 		}
 	}
 
+	Py_DECREF(type);
 	Py_RETURN_NONE;
 }
 
@@ -279,10 +283,6 @@ static PyObject *request_read_edge_events(request_object *self, PyObject *args)
 		max_events = 64;
 	}
 
-	type = Py_gpiod_GetGlobalType("EdgeEvent");
-	if (!type)
-		return NULL;
-
 	Py_BEGIN_ALLOW_THREADS;
 	ret = gpiod_line_request_read_edge_events(self->request,
 						 self->buffer, max_events);
@@ -296,10 +296,17 @@ static PyObject *request_read_edge_events(request_object *self, PyObject *args)
 	if (!events)
 		return NULL;
 
+	type = Py_gpiod_GetModuleAttrString("gpiod.edge_event", "EdgeEvent");
+	if (!type) {
+		Py_DECREF(events);
+		return NULL;
+	}
+
 	for (i = 0; i < num_events; i++) {
 		event = gpiod_edge_event_buffer_get_event(self->buffer, i);
 		if (!event) {
 			Py_DECREF(events);
+			Py_DECREF(type);
 			return NULL;
 		}
 
@@ -311,6 +318,7 @@ static PyObject *request_read_edge_events(request_object *self, PyObject *args)
 				gpiod_edge_event_get_line_seqno(event));
 		if (!event_obj) {
 			Py_DECREF(events);
+			Py_DECREF(type);
 			return NULL;
 		}
 
@@ -318,10 +326,12 @@ static PyObject *request_read_edge_events(request_object *self, PyObject *args)
 		if (ret) {
 			Py_DECREF(event_obj);
 			Py_DECREF(events);
+			Py_DECREF(type);
 			return NULL;
 		}
 	}
 
+	Py_DECREF(type);
 	return events;
 }
 
-- 
2.34.1