Add caching for the default I2C bus

If no keyword arguments are provided, then the default bus is requested. If this happens multiple times (eg. the user has multiple devices on the default bus), then it's faster to do this caching.

Author: sfe-SparkFro

qwiic_i2c/__init__.py

@@ -84,11 +84,12 @@
 	except:
 		pass
 
+_default_driver = None
+
 #-------------------------------------------------
 # Exported method to get the I2C driver for the execution plaform. 
 #
 # If no driver is found, a None value is returned
-
 def getI2CDriver(*args, **argk):
 	"""
 	.. function:: getI2CDriver()
@@ -105,14 +106,25 @@ def getI2CDriver(*args, **argk):
 		>>> myData = i2cDriver.readByte(0x73, 0x34)
 	"""
 
+	# If no parameters are provided, return the default driver if we have it
+	global _default_driver
+	if len(argk) == 0 and _default_driver != None:
+		return _default_driver
+	
+	# Loop through all the drivers to find the one for this platform
 	for driverClass in _drivers:
-
-		# Does this class/driverd support this platform?
 		if driverClass.isPlatform():
-
-			# Yes - return the driver object
-			return driverClass(*args, **argk)
-
+			# Found it!
+			driver = driverClass(*args, **argk)
+
+			# If no parameters are provided, set this as the default driver
+			if len(argk) == 0:
+				_default_driver = driver
+			
+			# And return it
+			return driver
+	
+	# If we get here, we didn't find a driver for this platform
 	return None
 
 def get_i2c_driver(*args, **argk):