import warnings
import numpy as np
from salamanca import data
[docs]class Translator(object):
"""An object to translate between national currencies in different years
By default, inflation is calculated using GDP Deflators (though CPI is
available as well).
Currencies are assumed to be in MER. If in PPP, 'units' must be set
appropriately.
Calculation is formulated based on:
http://www.iiasa.ac.at/web/home/research/Flagship-Projects/Global-Energy-Assessment/GEA_Annex_II.pdf
"""
def __init__(self):
wb = data.WorldBank()
self._cpi = wb.to_wide(wb.cpi()).set_index('country')
self._gdp_deflator = wb.to_wide(wb.gdp_deflator()).set_index('country')
self._xr = wb.to_wide(wb.exchange_rate()).set_index('country')
self._ppp_to_mer = wb.to_wide(wb.ppp_to_mer()).set_index('country')
[docs] def inflation(self, iso, fromyr, toyr, method='deflator'):
"""Calculate inflation for a country
Parameters
----------
iso: str
a 3-letter ISO code
fromyr: int
the starting year
toyr: int
the ending year
method: str
one of: cpi, deflator (default: deflator)
"""
method = method.lower()
df = self._cpi if method == 'cpi' else self._gdp_deflator
x = df.loc[iso][toyr] / df.loc[iso][fromyr]
if np.isnan(x):
warnings.warn(
'Bad currency translation for {}, '
'falling back to US inflation rates'.format(iso))
x = self.inflation('USA', fromyr, toyr, method=method)
return x
def ppp_to_mer(self, iso, yr):
return self._ppp_to_mer.loc[iso][yr]
def mer_to_ppp(self, iso, yr):
return 1.0 / self._ppp_to_mer.loc[iso][yr]
[docs] def exchange(self, x, iso=None, yr=None, units='MER',
fromiso=None, fromyr=None,
toiso=None, toyr=None,
inusd=False, inflation_method='deflator'):
"""Exchange currency from one country/year to another.
Parameters
----------
x: float
quantity of currency
iso: str, optional
a 3-letter ISO code
yr: int, optional
the year
units: str, optional
current currency units
one of: PPP or MER
fromiso: str, optional
a 3-letter ISO code for the origin country
fromyr: int, optional
the year initial year
toiso: str, optional
a 3-letter ISO code for the destination country
fromyr: int, optional
the year final year
inusd: bool, optional
return currency in USD of the final year
inflation_method: str, optional
the argument to provide to `inflation()`
"""
fromiso = fromiso or iso
fromiso = fromiso.upper()
fromyr = fromyr or yr
fromyr = int(fromyr)
toiso = toiso or 'USA'
toiso = toiso.upper()
toyr = toyr or yr
toyr = int(toyr)
units = units.upper()
# is using special inusd option, do full calculation and return
if inusd:
if iso is None:
raise ValueError(
'iso parameter must have a value if usd=True')
savex = x
x = self.exchange(x, fromiso='USA', toiso=iso,
yr=fromyr, units=units)
x *= self.inflation(iso, fromyr, toyr, method=inflation_method)
x = self.exchange(x, fromiso=iso, toiso='USA',
yr=toyr, units=units)
return x
# otherwise, assume currencies are in isos of origin
if fromyr == toyr:
# xr is the market exchange rate
xr_1 = self._xr.loc[fromiso][fromyr]
xr_2 = self._xr.loc[toiso][toyr]
if units == 'PPP':
# multiply by ratio of ppp conversion factor to market exchange
# rate, see http://data.worldbank.org/indicator/PA.NUS.PPPC.RF
xr_1 *= self._ppp_to_mer.loc[fromiso][fromyr]
xr_2 *= self._ppp_to_mer.loc[toiso][toyr]
x *= xr_2 / xr_1
elif iso is not None:
# only account for inflation in same country, no exchanging
x *= self.inflation(iso, fromyr, toyr, method=inflation_method)
else:
# account for exchange rate and inflation
x = self.exchange(x, fromiso=fromiso, toiso=toiso,
yr=fromyr, units=units)
x *= self.inflation(toiso, fromyr, toyr, method=inflation_method)
return x
