library updates!

[ladyada]

if const's have underlines, they wont be exposed outside the library, which i think makes sense for all the consts right? so instead of
TSL2561_DEFAULT_ADDRESS = const(0x39)
do
_TSL2561_DEFAULT_ADDRESS = const(0x39)

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init should check the id and raise an RuntimeError if the chip is not found, the id() function can be inlined if you like - see https://github.com/adafruit/Adafruit_CircuitPython_BMP280/blob/master/adafruit_bmp280.py#L67

---

i know @tannewt mentioned changing lux to light but i actually just changed it back again (lux is a formal SI spec, light is just monotonic light measurements) so please make the property back to 'lux' (sorry!)

[caternuson]

My understanding is this is only a convention:
https://docs.python.org/3/tutorial/classes.html#private-variables
If we are going to do this, maybe it should be added to the style guide?

---

OK

---

Ha! It would appear we agree on this:
adafruit/circuitpython#314 (comment)

[dhalbert]

In MicroPython/CircuitPython, adding the underscore actually prevents the name from going in the module dictionary. This is documented, but somewhat obscurely:

http://circuitpython.readthedocs.io/en/2.x/docs/reference/constrained.html?highlight=underscore

This RAM can be saved by prepending the name with an underscore as in _COLS: this symbol is not visible outside the module so will not occupy RAM.

http://circuitpython.readthedocs.io/en/2.x/docs/library/micropython.html?highlight=underscore

... if a constant begins with an underscore then it is hidden, it is not available as a global variable, and does not take up any memory during execution.

[caternuson]

So it's a micro/cp thing only? Just did this with CP 2.1:
foo.py:

SOME_CONST = 23
_SOME_CONST = 42

and then:

>>> import foo
>>> dir(foo)
['SOME_CONST', '_SOME_CONST', '__name__', '__file__']
>>> foo._SOME_CONST
42
>>> foo._SOME_CONST = 99
>>> foo._SOME_CONST
99

[ladyada]

i believe it is only when we mpy the file

[caternuson]

just tried. same behavior.

[dhalbert]

Sorry, I was half-wrong. It's when you use const() and there's an underscore. It's true for both .py and .mpy (just tested):

from micropython import const
PUBLIC = const(2)
_PRIVATE = const(3)

try that

[dhalbert]

const() can only be an integer expression - nothing else. I apologize for the misleading information earlier.

[caternuson]

yep. that's it.
foo.py

from micropython import const
SOME_CONST = const(23)
_SOME_CONST = const(42)

def foo():
    print("{0} {1}".format(SOME_CONST, _SOME_CONST))

REPL:

>>> import foo
>>> dir(foo)
['const', 'SOME_CONST', 'foo', '__file__', '__name__']
>>> foo.foo()
23 42

[caternuson]

How do we deal with non-integers?
https://github.com/adafruit/Adafruit_CircuitPython_TSL2561/blob/master/adafruit_tsl2561.py#L45

[dhalbert]

Use an underscore for consistency and as notice that it's meant to be private. Maybe someday const will work on other than integers.

[caternuson]

Is that the answer, or a suggestion? Sounds like we should add this to the design guide.

[ladyada]

i think both? :) we're updating the design guide ASAP, i just learned about this const stuff yesterday :D

[caternuson]

I think all three points in original post have been fixed, so closing.