rate limiting

get_foo.py

### Q1: Rate Limiting
# ==========================

# Say you have a function called `get_foo`. 
# The rate limit forbids it from being called more than 12 times a minute. 
# How do you properly rate limit this? Assume it's being called synchronously (from just one thread).


import requests
def get_foo():
    return requests.get("https://my-api.com/asdf")

# Solution: sliding window over time series

import time

bucket = []

def rate_limited_get_foo():

    # time.monotonic() only increases, is ideal.
    # time.time() tracks system clock and can jump backward
    now = time.monotonic()
    t0 = now - 60
    bucket[:] = [t for t in bucket if t > t0]

    if len(bucket) >= 12:
        raise Exception("Rate limit exceeded")

    bucket.append(now)
    result = get_foo()
    return result

# note: you could also use a deque here. I find this more readable.
# note: [:] mutates the list in place, keeping the reference.