Merge pull request #801 from gpiozero/native-warn-515

Warn users when falling back to NativeFactory, close #515

gpiozero/devices.py

@@ -62,10 +62,17 @@
     GPIOPinMissing,
     GPIOPinInUse,
     GPIODeviceClosed,
+    NativePinFactoryFallback,
     PinFactoryFallback,
     )
 from .compat import frozendict
 
+native_fallback_message = (
+'Falling back to the experimental pin factory NativeFactory because no other '
+'pin factory could be loaded. For best results, install RPi.GPIO or pigpio. '
+'See https://gpiozero.readthedocs.io/en/stable/api_pins.html for more information.'
+)
+
 
 class GPIOMeta(type):
     # NOTE Yes, this is a metaclass. Don't be scared - it's a simple one.
@@ -272,7 +279,10 @@ def _default_pin_factory():
                 try:
                     mod_name, cls_name = entry_point.split(':', 1)
                     module = __import__(mod_name, fromlist=(cls_name,))
-                    return getattr(module, cls_name)()
+                    pin_factory = getattr(module, cls_name)()
+                    if name == 'native':
+                        warnings.warn(NativePinFactoryFallback(native_fallback_message))
+                    return pin_factory
                 except Exception as e:
                     warnings.warn(
                         PinFactoryFallback(

gpiozero/exc.py

@@ -207,6 +207,9 @@ class PinWarning(GPIOZeroWarning):
 class PinFactoryFallback(PinWarning):
     "Warning raised when a default pin factory fails to load and a fallback is tried"
 
+class NativePinFactoryFallback(PinWarning):
+    "Warning raised when all other default pin factories fail to load and NativeFactory is used"
+
 class PinNonPhysical(PinWarning):
     "Warning raised when a non-physical pin is specified in a constructor"