Python海象运算符:=的具体实现

import datetime

person = {'name': 'Alice', 'birthyear': 1997}
currentyear = datetime.datetime.now().year

if birthyear := person.get('birthyear'):
    print(f'{currentyear - birthyear} years old')

# 传统写法
if person.get('birthyear'):
    birthyear = person['birthyear']  # 调多一次
    print(f'{currentyear - birthyear} years old')

with open('requirements.txt', encoding='utf-8') as f:
    while line := f.readline():
        print(line)

# 传统写法
with open('requirements.txt', encoding='utf-8') as f:
    while True:
        line = f.readline()
        if not line:
            break
        print(line)

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

squares = [squared for num in numbers if (squared := num ** 2) > 10]  # 计算平方值大于10的结果
print(squares)

# 传统写法
squares = [num ** 2 for num in numbers if num ** 2 > 10]
print(squares)

import re

text = 'Date: 2023-10-05'

if (match := re.search(r'(\d{4})-(\d{2})-(\d{2})', text)):
    year, month, day = match.groups()
    print(f'{year}-{month}-{day}')

# 传统写法
match = re.search(r'(\d{4})-(\d{2})-(\d{2})', text)
if match:
    year, month, day = match.groups()
    print(f'{year}-{month}-{day}')

import timeit
import random

# 10万个随机整数，计算平方值并筛选大于2500的元素
data = [random.randint(1, 100) for _ in range(100000)]


def traditional_method():
    """传统写法"""
    return [x ** 2 for x in data if x ** 2 > 2500]


def walrus_method():
    """海象运算符写法"""
    return [sq for x in data if (sq := x ** 2) > 2500]


traditional_time = timeit.timeit(traditional_method, number=100)
walrus_time = timeit.timeit(walrus_method, number=100)

print(f'传统写法耗时: {traditional_time:.4f} 秒')
print(f'海象运算符耗时: {walrus_time:.4f} 秒')
print(f'性能提升: {((traditional_time - walrus_time) / traditional_time) * 100:.2f}%')
# 传统写法耗时: 2.0772 秒
# 海象运算符耗时: 1.5260 秒
# 性能提升: 26.53%