variable scope of class objects

[JonRob]

@Dennis,


Thanks for your example.  My structure is very similar.  Perhaps I was
reading too much into Luca's below statement regarding declaring
variables.

Regards,
JonRob




    Luca wrote...
>Please, note that declaring a variable in the constructor is only a 
>convention: in Python you can add a variable to an object of a class 
>wherever you want in your code (even if it is very dangerous and 
>discouraged).


 





On Tue, 20 Oct 2015 20:18:35 -0400, Dennis Lee Bieber
<wlfraed at ix.netcom.com> wrote:

>On Tue, 20 Oct 2015 17:33:21 -0400, JonRob at mail.python.org declaimed the
>following:
>
>>
>>
>>Hello Luca,
>>
>>I very much appreciated your comments.  And I understand the
>>importance of "doing something right"  (i.e. convention).
>>
>>This leads me to another question.
>>
>>Because I am interfacing with an I2C sensor I have many register
>>definations to include (30 register addresses and  26 Variables to be
>>red from some of those registers.
>>In your comment you mentioned that convention is to declare variables
>>(and constants?)  in the construction (__ini__).
>>I am concerned that the sheer number of varialbe / constants would
>>make it difficult to read.
>>
>
>	"Constants" are typically defined at module level, using all capitals
>as a hint to the reader (Python does not have anything that one might
>consider a true constant -- other than the language defined singletons:
>None, and maybe by now True and False).
>
>	Register addresses are likely "constants". Not sure about your "26
>Variables"... Do they map directly to registers, or are they extracted as
>fields from the values returned -- that is, a register may have two or more
>"variables"? Do you read ALL registers on command and hold the values (note
>my usage -- values can be held in lists or dictionaries using a single
>"variable") for later retrieval by the user, or only read A register on
>command by the user and return that value.
>
>-=-=-=-=-
>#	registers for a fictitious motion sensor
>GYROXREG = 0x0010
>GYROYREG = 0x0011
>GYROZREG = 0x0001
>...
>MAGZREG = 0x0100
>
>class SensorA(I2C):	#I'm assuming class I2C provides read/write functions
>	_registers = [GYROXREG, GYROYREG, GYROZREG,
>					..., MAGZREG]
>	def __init__(self, SCLpin, SDApin, slaveAddress):
>		self._SCL = SCLpin
>		self._SDA = SDApin
>		self._addr = slaveAddress
>		self.update()	#initial load of values
>	def update(self):
>		#basically a loop over all addresses
>		#I'm not going to try to pseudo code the full I2C protocol
>		self.values = {}	#yes, a dictionary
>		for reg in _registers:
>			aValue = self.read(self._SCL, self._SDA, self._addr, reg)
>					#inherited from I2C class
>			self.values[reg] = aValue
>....
>
>mySensor = SensorA(21, 22, 0x6)
>
>while True
>	mySensor.update()
>	print ("Gyro X: %s, Y: %s, Z: %s"
>			% (mySensor.values[GYROXREG],
>				mySensor.values[GYROYREG],
>				mySensor.values[GYROZREG]))
>	time.sleep(1.0)
>
>
>			
>