variable scope of class objects

[Luca Menegotto]

Il 19/10/2015 20:39, JonRob ha scritto:

> I (think) I understand that in the below case, the word self could be
> replaced with "BME280" to explicitly call out a variable.
>
> But even still I don't know how explicit call out effects the scope of
> a variable.

These two statements make me think you come from C++ or something similar.

In Python you can declare variables at class level, but this declaration 
must NOT be interpreted in the same manner of a similar declaration in 
C++: they remain at the abstract level of a class, and they have nothing 
to do with an instance of a class (in fact, to be correctly invoked, 
they must be preceeded by the class name).

'self' (or a similar representation, you could use 'this' without 
problem) gives you access to the instance of the class, even in the 
constructor; it is important, because the constructor is the place where 
instance variables should be defined. Something like this:

class foo:
     # invoke with foo._imAtClassLevel
     _imAtClassLevel = 10

     def __init__(self):
         #  need to say how this must be invoked?
         self._imAtInstanceLevel = 0

no confusion is possible, because:

class foo2:
     _variable = 1000

     def __init__(self):
         # let's initialize an instance variable with
         # a class variable
         self._variable = foo2._variable

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).

-- 
Ciao!
Luca