Use unit prefix only instead of full unit

[laborleben]

instead set_voltage(self, channel, value, unit='mV') use set_voltage(self, channel, value, unit='m').

Makes things easier when comes to abstraction. We can also do some unit conversion based on a new class that we can put inside utils. The conversion is then based on a dict like that one:
_prefix = {'y': 1e-24, # yocto
'z': 1e-21, # zepto
'a': 1e-18, # atto
'f': 1e-15, # femto
'p': 1e-12, # pico
'n': 1e-9, # nano
'u': 1e-6, # micro
'm': 1e-3, # mili
'c': 1e-2, # centi
'd': 1e-1, # deci
'k': 1e3, # kilo
'M': 1e6, # mega
'G': 1e9, # giga
'T': 1e12, # tera
'P': 1e15, # peta
'E': 1e18, # exa
'Z': 1e21, # zetta
'Y': 1e24, # yotta
}
also check http://stackoverflow.com/questions/10969759/python-library-to-convert-between-si-unit-prefixes.

[laborleben]

We can stay compatible to the old interface by just evaluating the first char.

[themperek]

full ack

[DavidLP]

I would not add a unit feature at all. It should be understood that all is in SI base units. Adding a e.g. e-3 at the base unit should be no issue. Otherwise one can only understand any value with the unit string. At least I would make this a not mandatory API feature, but an optional way to define values. And the standard unit should be SI base units.

[laborleben]

depends, actually I can live without that feature. Others are using it.
However, implementing the conversion into every function is a waste of code. It can also be, that a conversion is needed for a DAC or ADC (wich is not using SI base unit).

[DavidLP]

A conversion for a ADC/DAC? What is that? ADC/DAC is just a value and no unit at all.

[themperek]

You do not want to thing what is 1.273V in DAC units. And calibration on
top.

On Sat, Mar 14, 2015 at 6:15 PM, D.-L.Pohl [email protected] wrote:

A conversion for a ADC/DAC? What is that? ADC/DAC is just a value and no
unit at all.

—
Reply to this email directly or view it on GitHub
#10 (comment).

[DavidLP]

Now we are talking about calibration and not units ;-). But for calibration data it is much better to have the SI base units only, otherwise some calibrations will be in mV, some in V...
To say set_voltage(1.273) is what I would prefer. How this is translated to a DAC value is irrelevant.

[themperek]

One does not go against other we assume we use default Si unit as default so e-3 etc will work.
And we have optional unit parameter.
Would this work? Does not break current situation.

[themperek]

http://pint.readthedocs.io/

[themperek]

We do this?