8个让Python代码效率翻倍的简单技巧

# 老掉牙的写法
temp = a
a = b
b = temp

# 运行一下试试：
a, b = 3, 5
print(f"交换前：a={a}, b={b}")
a, b = b, a  # 这行就够了！
print(f"交换后：a={a}, b={b}")

# 老式写法
new_names = []
for name in files:
    if name.endswith('.txt'):
        new_names.append(name.replace('.txt', '.md'))

# 来测试一下：
files = ['笔记1.txt', '笔记2.txt', '照片.jpg']
new_names = [name.replace('.txt', '.md') for name in files if name.endswith('.txt')]
print(f"处理后的文件名：{new_names}")

# 容易出错的写法
try:
    value = user_data['age']
except KeyError:
    value = 0

# 实战体验：
user_data = {'name': '小明'}
age = user_data.get('age', 18)  # 找不到就返回18
print(f"用户年龄：{age}")

# 各种魔法数字，看得头晕
if user_status == 0:
    print("未注册")
elif user_status == 1:
    print("已注册")
elif user_status == 2:
    print("已认证")

from enum import Enum

class UserStatus(Enum):
    UNREGISTERED = 0
    REGISTERED = 1
    VERIFIED = 2

# 实际使用起来很清晰
status = UserStatus.REGISTERED
print(f"用户状态：{status.name}")

if grade >= 90:
    level = "A"
elif grade >= 80:
    level = "B"
elif grade >= 70:
    level = "C"
else:
    level = "D"

# 实战测试：
grade_map = {
    lambda x: x >= 90: "A",
    lambda x: 80 <= x < 90: "B",
    lambda x: 70 <= x < 80: "C",
    lambda x: x < 70: "D"
}

def get_level(score):
    return next(v for k, v in grade_map.items() if k(score))

print(f"85分的等级：{get_level(85)}")

# 又臭又长的老写法
name = data['user']['profile']['name']

from functools import reduce
from operator import getitem

def deep_get(dictionary, keys, default=None):
    return reduce(lambda d, key: d.get(key, default) if isinstance(d, dict) else default, 
                 keys.split('.'), dictionary)

# 实战一下：
data = {
    'user': {
        'profile': {
            'name': '张三',
            'age': 25
        }
    }
}

name = deep_get(data, 'user.profile.name')
print(f"用户名：{name}")

f = open('data.txt', 'r')
# 处理文件
f.close()  # 经常忘记关闭

# 实战演示：
with open('demo.txt', 'w') as f:
    f.write('这才是正确的打开方式！')
print("文件已自动关闭，无需担心!")

def create_user(name, age=None, city=None, hobby=None):
    if age is None:
        age = 18
    if city is None:
        city = "北京"
    # ...更多判断

def create_user(**kwargs):
    defaults = {
        'age': 18,
        'city': '北京',
        'hobby': '编程'
    }
    params = {**defaults, **kwargs}
    return params

# 测试一下：
user1 = create_user(name='小明')
user2 = create_user(name='小红', age=20)
print(f"用户1：{user1}")
print(f"用户2：{user2}")