docs: Add example & info about log.add() exception when full.

docs/log.rst

@@ -95,6 +95,10 @@ Functions
     Labels previously specified and not present in a call to this function will
     be skipped with an empty value in the log row.
 
+    :raise OSError: When the log is full this function raises an ``OSError``
+        exception with error code 28 ``ENOSPC``, which indicates there is no
+        space left in the device.
+
 Examples
 ========
 

examples/data-logging.py

@@ -7,26 +7,36 @@
 # Send each data row to the serial output
 log.set_mirroring(True)
 
+continue_logging = True
+
 # This decorator schedules this function to run every 10s 50ms
 @run_every(s=10, ms=50)
 def log_data():
     """Log the temperature and light level, and display an icon."""
-    log.add(temp=temperature(), brightness=display.read_light_level())
-    display.show(Image.SURPRISED)
-    sleep(500)
+    global continue_logging
+    if continue_logging:
+        display.show(Image.SURPRISED)
+        try:
+            log.add(temp=temperature(), brightness=display.read_light_level())
+        except OSError:
+            continue_logging = False
+            display.scroll("Log full")
+        sleep(500)
 
 while True:
     if button_a.is_pressed() and button_b.is_pressed():
-        display.show(Image.MEH)
+        display.show(Image.CONFUSED)
         # Delete the log file using the "full" options, which takes
         # longer but ensures the data is wiped from the device
         log.delete(full=True)
+        continue_logging = True
     elif button_a.is_pressed():
         display.show(Image.HAPPY)
-        # Log only the light level, the temp entry will be empty
+        # Log only the light level, the temp entry will be empty. If the log
+        # is full this will throw an exception and the programme will stop
         log.add({
             "brightness": display.read_light_level()
         })
     else:
-        display.show(Image.CONFUSED)
+        display.show(Image.ASLEEP)
     sleep(500)