Python 50个实用代码片段，优雅高效

a, b = 1, 2
a, b = b, a  # 交换变量值
print(a, b)  # 输出: 2 1

x = 5
print(1 < x < 10)  # 输出: True

age = 20
status = "成年" if age >= 18 else "未成年"
print(status)  # 输出: 成年

text = "Python"
reversed_text = text[::-1]
print(reversed_text)  # 输出: nohtyP

items = [1, 2, 2, 3, 4, 4, 5]
unique_items = list(set(items))
print(unique_items)  # 输出: [1, 2, 3, 4, 5]

squares = [x**2 for x in range(10)]
print(squares)  # 输出: [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

even_squares = [x**2 for x in range(10) if x % 2 == 0]
print(even_squares)  # 输出: [0, 4, 16, 36, 64]

nested_list = [[1, 2], [3, 4], [5, 6]]
flat_list = [item for sublist in nested_list for item in sublist]
print(flat_list)  # 输出: [1, 2, 3, 4, 5, 6]

numbers = [3, 1, 4, 1, 5, 9, 2]
max_val = max(numbers)
min_val = min(numbers)
print(f"最大值: {max_val}, 最小值: {min_val}")

data = [5, 2, 8, 1, 9]
data.sort()  # 升序排序
print(data)  # 输出: [1, 2, 5, 8, 9]

data.sort(reverse=True)  # 降序排序
print(data)  # 输出: [9, 8, 5, 2, 1]

squares_dict = {x: x**2 for x in range(5)}
print(squares_dict)  # 输出: {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

dict1 = {'a': 1, 'b': 2}
dict2 = {'c': 3, 'd': 4}
merged = {**dict1, **dict2}
print(merged)  # 输出: {'a': 1, 'b': 2, 'c': 3, 'd': 4}

original = {'a': 1, 'b': 2, 'c': 3}
reversed_dict = {v: k for k, v in original.items()}
print(reversed_dict)  # 输出: {1: 'a', 2: 'b', 3: 'c'}

from collections import defaultdict

word_count = defaultdict(int)
words = ['apple', 'banana', 'apple', 'orange']
for word in words:    
word_count[word] += 1
print(dict(word_count))  # 输出: {'apple': 2, 'banana': 1, 'orange': 1}

from collections import OrderedDict
ordered = OrderedDict()
ordered['z'] = 1
ordered['a'] = 2
ordered['m'] = 3
print(list(ordered.keys()))  # 输出: ['z', 'a', 'm']

words = ['Hello', 'World', 'Python']
sentence = ' '.join(words)
print(sentence)  # 输出: Hello World Python

text = "apple,banana,orange"
fruits = text.split(',')
print(fruits)  # 输出: ['apple', 'banana', 'orange']

text = "I like Java"
new_text = text.replace("Java", "Python")
print(new_text)  # 输出: I like Python

name = "Alice"
age = 25
message = f"{name} is {age} years old"
print(message)  # 输出: Alice is 25 years old

filename = "document.pdf"
is_pdf = filename.endswith('.pdf')
is_doc = filename.startswith('doc')
print(f"PDF文件: {is_pdf}, 文档文件: {is_doc}")

def sum_numbers(*args):    
return sum(args)
result = sum_numbers(1, 2, 3, 4, 5)
print(result)  # 输出: 15

def create_profile(**kwargs):    
for key, value in kwargs.items():        
print(f"{key}: {value}")

create_profile(name="John", age=30, city="New York")

square = lambda x: x**2
print(square(5))  # 输出: 25

numbers = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x**2, numbers))
print(squared)  # 输出: [1, 4, 9, 16, 25]

from functools import lru_cache

@lru_cache(maxsize=None)
def fibonacci(n):    
if n < 2:        
return n    
return fibonacci(n-1) + fibonacci(n-2)

print(fibonacci(10))  # 输出: 55

def timer(func):    
import time    
def wrapper(*args, **kwargs):        
start = time.time()        
result = func(*args, **kwargs)        
end = time.time()        
print(f"函数 {func.__name__} 执行时间: {end-start:.2f}秒")        
return result    
return wrapper

@timer
def slow_function():    
time.sleep(1)

slow_function()

with open('example.txt', 'r', encoding='utf-8') as file:
    content = file.read()
    print(content)

with open('example.txt', 'r', encoding='utf-8') as file:
    for line in file:
        print(line.strip())

data = ["第一行", "第二行", "第三行"]
with open('output.txt', 'w', encoding='utf-8') as file:
    for line in data:
        file.write(line + '\n')

import json

# 写入JSON
data = {"name": "John", "age": 30}
with open('data.json', 'w') as f:    
json.dump(data, f)

# 读取JSON
with open('data.json', 'r') as f:    
loaded_data = json.load(f)    
print(loaded_data)

import csv

# 写入CSV
with open('data.csv', 'w', newline='') as file:    
writer = csv.writer(file)    
writer.writerow(['Name', 'Age', 'City'])    
writer.writerow(['Alice', 25, 'New York'])    
writer.writerow(['Bob', 30, 'London'])

# 读取CSV
with open('data.csv', 'r') as file:    
reader = csv.reader(file)    
for row in reader:        
print(row)

try:
    result = 10 / 0
except ZeroDivisionError:
    print("不能除以零!")

try:
    # 可能出错的代码
    number = int("abc")
except ValueError:
    print("值错误!")
except Exception as e:
    print(f"其他错误: {e}")

try:
    file = open('test.txt', 'r')
    content = file.read()
except FileNotFoundError:
    print("文件不存在!")
finally:
    file.close()  # 确保文件被关闭

class NegativeNumberError(Exception):    
pass

def check_positive(number):    
if number < 0:        
raise NegativeNumberError("数字不能为负")    
return number

try:    
check_positive(-5)
except NegativeNumberError as e:    
print(e)

class Timer:    
def __enter__(self):        
import time        
self.start = time.time()        
return self        

def __exit__(self, *args):        
self.end = time.time()        
print(f"耗时: {self.end-self.start:.2f}秒")

with Timer():    
# 需要计时的代码    
import time    
time.sleep(1)

from datetime import datetime

now = datetime.now()print(f"当前时间: {now}")print(f"格式化时间: {now.strftime('%Y-%m-%d %H:%M:%S')}")

from datetime import datetime, timedelta

start = datetime(2024, 1, 1)
end = datetime(2024, 1, 10)
difference = end - startprint(f"相差天数: {difference.days}")

import timefrom datetime import datetime

timestamp = time.time()print(f"当前时间戳: {timestamp}")
dt = datetime.fromtimestamp(timestamp)
print(f"转换后的时间: {dt}")

from datetime import datetimeimport pytz

utc_time = datetime.now(pytz.utc)beijing_time = utc_time.astimezone(pytz.timezone('Asia/Shanghai'))
print(f"北京时间: {beijing_time}")

from datetime import datetime

date_string = "2024-01-15 14:30:00"
parsed_date = datetime.strptime(date_string, '%Y-%m-%d %H:%M:%S')
print(f"解析后的日期: {parsed_date}")

# 生成器节省内存
large_sum = sum(x for x in range(1000000))
print(f"总和: {large_sum}")

class CountDown:    
def __init__(self, start):        
self.current = start        
def __iter__(self):        
return self        

def __next__(self):        
if self.current <= 0:            
raise StopIteration        
self.current -= 1        
return self.current + 1

for num in CountDown(5):    
print(num)

class FileManager:    
def __init__(self, filename, mode):        
self.filename = filename        
self.mode = mode        
self.file = None        

def __enter__(self):        
self.file = open(self.filename, self.mode)        
return self.file        

def __exit__(self, exc_type, exc_val, exc_tb):        
if self.file:            
self.file.close()

with FileManager('test.txt', 'w') as f:    
f.write('Hello, World!')

class Person:    
def __init__(self, name):        
self._name = name        

@property    
def name(self):        
return self._name        

@name.setter    
def name(self, value):        
if not value:            
raise ValueError("姓名不能为空")        
self._name = value

person = Person("Alice")
print(person.name)
person.name = "Bob"
print(person.name)

class Calculator:    
@staticmethod    
def add(x, y):        
return x + y        

@classmethod    
def multiply(cls, x, y):        
return x * y

print(Calculator.add(5, 3))      # 输出: 8print(Calculator.multiply(5, 3)) # 输出: 15

from tqdm import tqdmimport time

for i in tqdm(range(100)):    
time.sleep(0.1)  # 模拟耗时操作

import sys

def show_memory_usage(var_name, variable):    
size = sys.getsizeof(variable)    
print(f"{var_name} 占用内存: {size} 字节")

large_list = list(range(100000))
show_memory_usage("large_list", large_list)

import timeit

code_to_test = """sum_result = sum(range(1000))"""
execution_time = timeit.timeit(code_to_test, number=1000)
print(f"执行时间: {execution_time:.4f} 秒")

import os

# 读取环境变量
python_path = os.getenv('PYTHONPATH')
print(f"Python路径: {python_path}")

# 设置环境变量（当前进程）
os.environ['MY_VAR'] = 'my_value'

import sys

# 简单参数解析
if len(sys.argv) > 1:    
print(f"接收到的参数: {sys.argv[1:]}")
else:    
print("没有提供参数")

# 使用argparse进行高级解析
import argparse
parser = argparse.ArgumentParser(description='示例程序')
parser.add_argument('--name', type=str, help='你的姓名')
parser.add_argument('--age', type=int, help='你的年龄')

args = parser.parse_args()
if args.name and args.age:    
print(f"你好 {args.name}, 你 {args.age} 岁了")