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#!/usr/bin/env python3
"""
An example of using the [time-machine](https://github.com/adamchainz/time-machine) library for backtesting,
e.g., testing with cached responses that were available at an arbitrary time in the past.
"""
from datetime import UTC, datetime
import requests
import time_machine
from requests_cache import CachedSession, set_response_defaults
class BacktestCachedSession(CachedSession):
def request(self, method: str, url: str, **kwargs):
response = super().request(method, url, **kwargs)
# Response was cached after the (simulated) current time, so ignore it and send a new request
if response.created_at and response.created_at > datetime.now(UTC):
new_response = requests.request(method, url, **kwargs)
return set_response_defaults(new_response)
else:
return response
def demo():
session = BacktestCachedSession()
response = session.get('https://httpbin.org/get')
response = session.get('https://httpbin.org/get')
assert response.from_cache is True
# Response was not cached yet at this point, so we should get a fresh one
with time_machine.travel(datetime(2020, 1, 1)):
response = session.get('https://httpbin.org/get')
assert response.from_cache is False
if __name__ == '__main__':
demo()
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