7edf3fee67
As the Quantity class has an expensive __getattr__ this check was having a measurable performance hit. Close #251
1.9 KiB
Different Unit Systems (and default units)
Pint Unit Registry has the concept of system, which is a group of units
>>> import pint >>> ureg = pint.UnitRegistry(system='mks') >>> ureg.system 'mks'
This has an effect in the base units. For example:
>>> q = 3600. * ureg.meter / ureg.hour >>> q.to_base_units() <Quantity(1.0, 'meter / second')>
We can take a look for the available systems
>>> ureg.systems frozenset({'US', 'mks', 'imperial', 'cgs'})
But if you change to cgs:
>>> ureg.system = 'cgs' >>> q.to_base_units() <Quantity(100.0, 'centimeter / second')>
or more drastically to:
>>> ureg.system = 'imperial' >>> '{:.3f}'.format(q.to_base_units()) '1.094 yard / second'
..warning: In versions previous to 0.7 to_base_units returns quantities in the units of the definition files (which are called root units). For the definition file bundled with pint this is meter/gram/second. To get back this behaviour use to_root_units, set ureg.system = None
You can also use system to narrow down the list of compatible units:
>>> ureg.system = 'mks' >>> ureg.get_compatible_units('meter') frozenset({<Unit('light_year')>, <Unit('angstrom')>, <Unit('US_survey_mile')>, <Unit('yard')>, <Unit('US_survey_foot')>, <Unit('US_survey_yard')>, <Unit('inch')>, <Unit('rod')>, <Unit('mile')>, <Unit('barleycorn')>, <Unit('foot')>, <Unit('mil')>})
>>> ureg.system = 'imperial' >>> ureg.get_compatible_units('meter') frozenset({<Unit('US_survey_mile')>, <Unit('angstrom')>, <Unit('inch')>, <Unit('light_year')>, <Unit('barleycorn')>, <Unit('mile')>, <Unit('US_survey_foot')>, <Unit('rod')>, <Unit('US_survey_yard')>, <Unit('yard')>, <Unit('mil')>, <Unit('foot')>})
>>> ureg.imperial.pint bla
>>> ureg.us.pint