How to Build a Sidecar Logging Proxy in Python

import logging
import time
from datetime import datetime


class LoggingProxy:
    """Sidecar-style proxy that logs all calls to a wrapped object."""

    def __init__(self, target, log_file="proxy.log"):
        self._target = target
        logging.basicConfig(
            filename=log_file,
            level=logging.INFO,
            format="%(asctime)s - %(message)s",
        )
        self.logger = logging.getLogger("proxy_sidecar")

    def __getattr__(self, name):
        attr = getattr(self._target, name)

        if callable(attr):
            def wrapper(*args, **kwargs):
                start = time.time()
                self.logger.info(f"CALL {name} args={args} kwargs={kwargs}")
                result = attr(*args, **kwargs)
                elapsed = time.time() - start
                self.logger.info(f"RETURN {name} result={result} elapsed={elapsed:.4f}s")
                return result
            return wrapper
        return attr


class Calculator:
    def add(self, a, b):
        return a + b

    def multiply(self, a, b):
        return a * b


if __name__ == "__main__":
    calc = Calculator()
    proxy = LoggingProxy(calc, "proxy.log")
    print(f"add(2, 3) = {proxy.add(2, 3)}")
    print(f"multiply(4, 5) = {proxy.multiply(4, 5)}")
    print("Sidecar log written to proxy.log")