Measure the elapsed time of a block of code using Python

perf.py

import time


class Watcher:
    """
    Measure the elapsed time of a block of code

    Usage:

    1. with statement:
    with Watcher("loading something"):
        # code to be measured

    2. context manager:
    w = Watcher("expensive operation")
    w.start()
    # code to be measured
    w.end()

    3. static method:
    w = Watcher.watch("doing something")
    # code to be measured
    w.end()
    """

    def __init__(self, message="Elapsed time"):
        self.start_time = None
        self.end_time = None
        self.elapsed_time = None
        self.message = message

    def start(self):
        self.start_time = time.time()

    def end(self):
        if self.start_time is None:
            raise RuntimeError("Timer has not been started.")
        self.end_time = time.time()
        self.elapsed_time = self.end_time - self.start_time
        print(f"{self.message}: {self.elapsed_time:.4f} seconds")

    def __enter__(self):
        self.start()
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        self.end()

    @classmethod
    def watch(cls, message):
        return cls(message)