用 Python 免费汇率 API
获取并转换汇率

from dataclasses import dataclass
from datetime import date
from decimal import Decimal, InvalidOperation

import requests
from requests.adapters import HTTPAdapter
from urllib3.util.retry import Retry


@dataclass(frozen=True)
class RateObservation:
    observed_on: date
    base: str
    quote: str
    rate: Decimal


def build_session() -> requests.Session:
    retry = Retry(
        total=4,
        connect=3,
        read=3,
        status=3,
        backoff_factor=0.5,
        status_forcelist=(429, 500, 502, 503, 504),
        allowed_methods=frozenset({"GET"}),
        respect_retry_after_header=True,
        raise_on_status=False,
    )
    session = requests.Session()
    session.mount("https://", HTTPAdapter(max_retries=retry))
    return session


def get_rate(
    session: requests.Session,
    base: str = "USD",
    quote: str = "EUR",
) -> RateObservation:
    base, quote = base.upper(), quote.upper()
    if not (len(base) == len(quote) == 3 and base.isalpha() and quote.isalpha()):
        raise ValueError("Currency codes must contain three letters")

    url = f"https://api.frankfurter.dev/v2/rate/{base}/{quote}"
    response = session.get(url, timeout=(3.05, 10))
    response.raise_for_status()
    data = response.json()

    required = {"date", "base", "quote", "rate"}
    if not required <= data.keys():
        raise ValueError("Unexpected exchange-rate response")
    if data["base"] != base or data["quote"] != quote:
        raise ValueError("Provider returned a different currency pair")

    try:
        observed_on = date.fromisoformat(data["date"])
        value = Decimal(str(data["rate"]))
    except (TypeError, ValueError, InvalidOperation) as exc:
        raise ValueError("Invalid date or exchange rate") from exc
    if not value.is_finite() or value <= 0:
        raise ValueError("Exchange rate must be a positive finite number")

    return RateObservation(observed_on, base, quote, value)


session = build_session()
rate = get_rate(session, "USD", "EUR")
print(rate.observed_on, rate.rate)

from decimal import Decimal, ROUND_HALF_UP

def convert_amount(amount, rate, minor_units=2):
    value = Decimal(str(amount)) * Decimal(str(rate))
    quantum = Decimal("1").scaleb(-minor_units)
    return value.quantize(quantum, rounding=ROUND_HALF_UP)

converted = convert_amount("125.50", rate.rate)
print(f"125.50 USD = {converted} EUR")