Merge pull request #59 from rsbohn/master

Support boards that don't have a fixed I2C bus.

Author: jepler

adafruit_seesaw/tftshield18.py

@@ -66,7 +66,12 @@ class TFTShield18(Seesaw):
         # TypeError: unsupported operand type(s) for <<: 'int' and '_MockObject'
         _button_mask = 0xFF
 
-    def __init__(self, i2c_bus=board.I2C(), addr=0x2E):
+    def __init__(self, i2c_bus=None, addr=0x2E):
+        if i2c_bus is None:
+            try:
+                i2c_bus = board.I2C()
+            except AttributeError as attrError:
+                raise ValueError("Board has no default I2C bus.") from attrError
         super().__init__(i2c_bus, addr)
         self.pin_mode(_TFTSHIELD_RESET_PIN, self.OUTPUT)
         self.pin_mode_bulk(self._button_mask, self.INPUT_PULLUP)