pint currency example

README.md

pint + currency_converter = ❤️

This gist is used to demonstrate a bug that I'm running into when trying to dynamically enable currency conversion in pint using currency conversion factors from currencyconverter.

Approach: dynamically add currencies to unit registry following the "full model" approach and add contexts programmatically to convert between any two pairs of units.

repro steps

1. install dependencies poetry install
2. run example script poetry run python hanging.py and notice that it works successfully.
3. run example script poetry run python hanging.py and notice that it hangs.

hanging.py

import itertools

import pint
import currency_converter

# create a currency converter instance to load all of the data
cc = currency_converter.CurrencyConverter()

# load custom units and instantiate Quantity base class that is used everywhere
ureg = pint.UnitRegistry()
for c in cc.currencies:
    ureg.define(f"{c} = [currency_{c}]")  # i.e. USD = [currency_USD]


# add programmatic context for currency conversion
currency_context = pint.Context("currency", defaults={"date": None})
currencies = list(cc.currencies)
for a, b in itertools.combinations(currencies, 2):
    def a2b(_ureg, x, date=None, a=a, b=b):
        return cc.convert(x.magnitude, a, b, date=date) * _ureg(b)

    def b2a(_ureg, x, date=None, a=a, b=b):
        return cc.convert(x.magnitude, b, a, date=date) * _ureg(a)

    currency_context.add_transformation(f"[currency_{a}]", f"[currency_{b}]", a2b)
    currency_context.add_transformation(f"[currency_{b}]", f"[currency_{a}]", b2a)
ureg.add_context(currency_context)

Quantity = ureg.Quantity

q = Quantity(1, currencies[0])
with ureg.context("currency"):
    for c in currencies:
        print(q)
        q = q.to(c)
    print(q)
    q = q.to(currencies[0])
    print(q)

poetry.lock

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[metadata]
lock-version = "2.0"
python-versions = "^3.11"
content-hash = "f46f25da15c5cc2c2314e4fbf46b14036675b84b237be3e3a41eacc3dec5050a"

pyproject.toml

[tool.poetry]
name = "pint+currency-converter"
version = "0.1.0"
description = ""
authors = ["Dean Malmgren <[email protected]>"]
readme = "README.md"

[tool.poetry.dependencies]
python = "^3.11"
pint = "^0.24.4"
currencyconverter = "^0.18.3"


[tool.poetry.group.dev.dependencies]
ipdb = "^0.13.13"

[build-system]
requires = ["poetry-core"]
build-backend = "poetry.core.masonry.api"

working.py

import itertools

import pint
import currency_converter

# create a currency converter instance to load all of the data
cc = currency_converter.CurrencyConverter()

# load custom units and instantiate Quantity base class that is used everywhere
ureg = pint.UnitRegistry()
for c in cc.currencies:
    ureg.define(f"{c} = [currency_{c}]")  # i.e. USD = [currency_USD]


# add programmatic context for currency conversion
currency_context = pint.Context("currency", defaults={"date": None})
currencies = ["USD", "EUR", "JPY", "DKK", "CAD"]
for a, b in itertools.combinations(currencies, 2):
    def a2b(_ureg, x, date=None, a=a, b=b):
        return cc.convert(x.magnitude, a, b, date=date) * _ureg(b)

    def b2a(_ureg, x, date=None, a=a, b=b):
        return cc.convert(x.magnitude, b, a, date=date) * _ureg(a)

    currency_context.add_transformation(f"[currency_{a}]", f"[currency_{b}]", a2b)
    currency_context.add_transformation(f"[currency_{b}]", f"[currency_{a}]", b2a)
ureg.add_context(currency_context)

Quantity = ureg.Quantity

q = Quantity(1, currencies[0])
with ureg.context("currency"):
    for c in currencies:
        print(q)
        q = q.to(c)
    print(q)
    q = q.to(currencies[0])
    print(q)