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units.py
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units.py
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"wraps pint in gpkit monomials"
try:
import pint
ureg = pint.UnitRegistry() # pylint: disable=invalid-name
ureg.define("USD = [money] = $")
pint.set_application_registry(ureg)
Quantity = ureg.Quantity
DimensionalityError = pint.DimensionalityError
except ImportError: # pint is not installed; provide dummy imports
ureg = DimensionalityError = None # pylint: disable=invalid-name
class Quantity:
"Dummy class for if pint is not installed"
def __init__(self, *_):
pass
QTY_CACHE = {}
def qty(unit):
"Returns a Quantity, caching the result for future retrievals"
if unit not in QTY_CACHE:
QTY_CACHE[unit] = Quantity(1, unit)
return QTY_CACHE[unit]
class GPkitUnits:
"Return Monomials instead of Quantitites"
division_cache = {}
multiplication_cache = {}
monomial_cache = {}
def __call__(self, unity):
"Returns a unit Monomial, caching the result for future retrievals"
from . import Monomial
if unity not in self.monomial_cache:
self.monomial_cache[unity] = Monomial(qty(unity))
return self.monomial_cache[unity]
__getattr__ = __call__
def of_division(self, numerator, denominator):
"Cached unit division. Requires Quantity inputs."
if numerator.units is denominator.units:
return 1
key = (id(numerator.units), id(denominator.units))
try:
return self.division_cache[key]
except KeyError:
if numerator.units and denominator.units:
conversion = numerator.units/denominator.units
else:
conversion = numerator.units or 1/denominator.units
try:
self.division_cache[key] = float(conversion)
except DimensionalityError:
raise DimensionalityError(numerator, denominator)
return self.division_cache[key]
def of_product(self, thing1, thing2):
"Cached unit division. Requires united inputs."
key = (thing1.units, thing2.units)
try:
return self.multiplication_cache[key]
except KeyError:
mul_units = qty((thing1*thing2).units)
try:
self.multiplication_cache[key] = (None, float(mul_units))
except DimensionalityError:
self.multiplication_cache[key] = (mul_units, None)
return self.multiplication_cache[key]
units = GPkitUnits()