How do I measure elapsed time in Python?

To measure elapsed time in Python, you can use the time module, which provides several high-resolution timers. Here’s a concise guide:

1. Basic Elapsed Time (Wall-Clock)

Use time.perf_counter() for precise measurements:

import time

start = time.perf_counter()
# Your code here
end = time.perf_counter()
elapsed = end - start
print(f"Elapsed time: {elapsed:.6f} seconds")

2. Reusable Context Manager

Encapsulate timing logic for cleaner code:

from contextlib import contextmanager
import time

@contextmanager
def timer():
    start = time.perf_counter()
    yield
    end = time.perf_counter()
    print(f"Time: {end - start:.6f} seconds")

# Usage:
with timer():
    # Code to time
    time.sleep(1)

3. CPU Time (Process Time)

Measure CPU time (ignoring sleep/wait time):

start = time.process_time()
# Code here
end = time.process_time()
print(f"CPU Time: {end - start:.6f} seconds")

4. Using timeit for Small Code Snippets

Benchmark code with the timeit module:

import timeit

code_to_test = """
result = sum(range(1000))
"""
time_taken = timeit.timeit(code_to_test, number=1000)
print(f"Time per loop: {time_taken / 1000:.6f} seconds")

Key Functions Comparison

Function	Use Case
time.perf_counter()	High-resolution wall-clock timing (best for most cases).
time.process_time()	CPU time (excludes sleep/system calls).
time.time()	Simple wall-clock time (less precise).
timeit.timeit()	Benchmark small code snippets with loops.

Example: Decorator for Function Timing

import time

def time_decorator(func):
    def wrapper(*args, **kwargs):
        start = time.perf_counter()
        result = func(*args, **kwargs)
        end = time.perf_counter()
        print(f"{func.__name__} took {end - start:.6f} seconds")
        return result
    return wrapper

@time_decorator
def my_function():
    time.sleep(2)

my_function()  # Output: "my_function took 2.000456 seconds"

Notes

• Precision: perf_counter() is monotonic and ideal for benchmarking.
• Avoid time.time() for short intervals due to lower resolution.
• Jupyter/IPython: Use %timeit magic command for quick snippets.

Choose the method that best fits your use case!