How to Build a Rate Limiter in Python

import time
import random

class RateLimiter:
    """Simple token bucket rate limiter for beginners."""
    
    def __init__(self, max_tokens=5, refill_rate=1.0):
        self.max_tokens = max_tokens
        self.tokens = max_tokens
        self.refill_rate = refill_rate  # tokens per second
        self.last_refill = time.monotonic()
    
    def _refill(self):
        now = time.monotonic()
        elapsed = now - self.last_refill
        self.tokens = min(self.max_tokens, self.tokens + elapsed * self.refill_rate)
        self.last_refill = now
    
    def acquire(self):
        """Try to take a token. Return True if allowed, False if rate-limited."""
        self._refill()
        if self.tokens >= 1:
            self.tokens -= 1
            return True
        return False


def fetch_data_with_retry(data_loader, retries=3, max_delay=2.0):
    """Fetch data with retry logic for failed attempts."""
    for attempt in range(retries):
        try:
            return data_loader()
        except Exception as e:
            wait = random.uniform(0.5, max_delay) * (attempt + 1)
            print(f"Attempt {attempt + 1} failed: {e}. Retrying in {wait:.1f}s...")
            time.sleep(wait)
    raise RuntimeError("All retry attempts exhausted")


if __name__ == "__main__":
    # Example usage
    limiter = RateLimiter(max_tokens=3, refill_rate=1)
    
    for i in range(5):
        if limiter.acquire():
            print(f"Request {i + 1}: allowed")
        else:
            print(f"Request {i + 1}: rate-limited")
    
    print("\nWaiting 2 seconds for refill...")
    time.sleep(2)
    
    if limiter.acquire():
        print("Request after refill: allowed")