Merge pull request #925 from gpiozero/863-cleanup-docs

Explain how to cleanup after exception, close #863

docs/faq.rst

@@ -268,6 +268,8 @@ This means that you can reuse the pin for another device, and that despite
 turning the LED on (and hence, the pin high), after calling
 :meth:`~Device.close` it is restored to its previous state (LED off, pin low).
 
+Read more about :ref:`migrating_from_rpigpio`.
+
 
 How do I use button.when_pressed and button.when_held together?
 ===============================================================

docs/migrating_from_rpigpio.rst

@@ -333,6 +333,22 @@ Pin state cleanup is explicit in RPi.GPIO, and is done manually with
 pin used, at the end of the script. Manual cleanup is possible by use of the
 :meth:`~Device.close` method on the device.
 
+Note that cleanup only occurs at the point of normal termination of the script.
+If the script exits due to a program error, cleanup will not be performed. To
+ensure that cleanup is performed after an exception is raised, the exception
+must be handled, for example::
+
+    from gpiozero import Button
+
+    btn = Button(4)
+
+    while True:
+        try:
+            if btn.is_pressed:
+                print("Pressed")
+        except KeyboardInterrupt:
+            print("Ending program")
+
 Read more in the relevant FAQ: :ref:`gpio-cleanup`