Python 快速参考手册

🚀 基础语法

变量和数据类型

# 基本数据类型
name = "Python"          # 字符串 (str)
age = 30                 # 整数 (int)
height = 5.9             # 浮点数 (float)
is_student = True        # 布尔值 (bool)
data = None              # 空值 (NoneType)

# 类型检查
print(type(name))        # <class 'str'>
print(isinstance(age, int))  # True

字符串操作

# 字符串基础
text = "Hello, World!"
print(len(text))         # 13
print(text.upper())      # HELLO, WORLD!
print(text.lower())      # hello, world!
print(text.replace("World", "Python"))  # Hello, Python!

# 字符串格式化
name = "Alice"
age = 25
print(f"My name is {name} and I'm {age} years old")
print("My name is {} and I'm {} years old".format(name, age))
print("My name is %s and I'm %d years old" % (name, age))

运算符

# 算术运算符
a, b = 10, 3
print(a + b)    # 13 (加法)
print(a - b)    # 7  (减法)
print(a * b)    # 30 (乘法)
print(a / b)    # 3.333... (除法)
print(a // b)   # 3  (整除)
print(a % b)    # 1  (取余)
print(a ** b)   # 1000 (幂运算)

# 比较运算符
print(a > b)    # True
print(a == b)   # False
print(a != b)   # True

# 逻辑运算符
print(True and False)   # False
print(True or False)    # True
print(not True)         # False

🔄 控制流

条件语句

# if-elif-else
score = 85
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
else:
    grade = "F"

# 三元运算符
result = "Pass" if score >= 60 else "Fail"

循环

# for 循环
for i in range(5):
    print(i)  # 0, 1, 2, 3, 4

for char in "Python":
    print(char)  # P, y, t, h, o, n

# while 循环
count = 0
while count < 5:
    print(count)
    count += 1

# 循环控制
for i in range(10):
    if i == 3:
        continue  # 跳过当前迭代
    if i == 7:
        break     # 退出循环
    print(i)

📊 数据结构

列表 (List)

# 创建和操作
fruits = ["apple", "banana", "orange"]
fruits.append("grape")           # 添加元素
fruits.insert(1, "kiwi")         # 插入元素
fruits.remove("banana")          # 删除元素
popped = fruits.pop()            # 弹出最后一个元素

# 列表推导式
squares = [x**2 for x in range(10)]
even_squares = [x**2 for x in range(10) if x % 2 == 0]

# 常用方法
print(len(fruits))               # 长度
print(fruits.index("apple"))     # 查找索引
print(fruits.count("apple"))     # 计数
fruits.sort()                    # 排序
fruits.reverse()                 # 反转

字典 (Dictionary)

# 创建和操作
person = {"name": "Alice", "age": 30, "city": "New York"}
person["email"] = "alice@example.com"  # 添加键值对
del person["city"]                     # 删除键值对

# 字典方法
print(person.keys())             # 获取所有键
print(person.values())           # 获取所有值
print(person.items())            # 获取所有键值对
print(person.get("phone", "N/A")) # 安全获取值

# 字典推导式
squares_dict = {x: x**2 for x in range(5)}

元组 (Tuple)

# 创建（不可变）
coordinates = (10, 20)
rgb = (255, 128, 0)

# 元组解包
x, y = coordinates
r, g, b = rgb

# 命名元组
from collections import namedtuple
Point = namedtuple('Point', ['x', 'y'])
p = Point(10, 20)
print(p.x, p.y)

集合 (Set)

# 创建和操作
numbers = {1, 2, 3, 4, 5}
numbers.add(6)                   # 添加元素
numbers.remove(3)                # 删除元素
numbers.discard(10)              # 安全删除（不存在不报错）

# 集合运算
set1 = {1, 2, 3, 4}
set2 = {3, 4, 5, 6}
print(set1 & set2)               # 交集 {3, 4}
print(set1 | set2)               # 并集 {1, 2, 3, 4, 5, 6}
print(set1 - set2)               # 差集 {1, 2}

🔧 函数

函数定义

# 基本函数
def greet(name):
    """问候函数"""
    return f"Hello, {name}!"

# 默认参数
def power(base, exponent=2):
    return base ** exponent

# 可变参数
def sum_all(*args):
    return sum(args)

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

# 函数调用
print(greet("Alice"))
print(power(3))          # 使用默认参数
print(power(3, 4))       # 指定参数
print(sum_all(1, 2, 3, 4, 5))
print_info(name="Bob", age=25, city="Paris")

Lambda 函数

# 匿名函数
square = lambda x: x**2
add = lambda x, y: x + y

# 与内置函数结合使用
numbers = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x**2, numbers))
evens = list(filter(lambda x: x % 2 == 0, numbers))

🏗️ 面向对象编程

类和对象

class Person:
    # 类属性
    species = "Homo sapiens"
    
    def __init__(self, name, age):
        # 实例属性
        self.name = name
        self.age = age
    
    def introduce(self):
        # 实例方法
        return f"Hi, I'm {self.name} and I'm {self.age} years old"
    
    @classmethod
    def from_birth_year(cls, name, birth_year):
        # 类方法
        age = 2024 - birth_year
        return cls(name, age)
    
    @staticmethod
    def is_adult(age):
        # 静态方法
        return age >= 18

# 使用类
person1 = Person("Alice", 30)
person2 = Person.from_birth_year("Bob", 1990)
print(person1.introduce())
print(Person.is_adult(16))

继承

class Animal:
    def __init__(self, name):
        self.name = name
    
    def speak(self):
        pass

class Dog(Animal):
    def speak(self):
        return f"{self.name} says Woof!"

class Cat(Animal):
    def speak(self):
        return f"{self.name} says Meow!"

# 多态
animals = [Dog("Buddy"), Cat("Whiskers")]
for animal in animals:
    print(animal.speak())

特殊方法

class Book:
    def __init__(self, title, pages):
        self.title = title
        self.pages = pages
    
    def __str__(self):
        return f"Book: {self.title}"
    
    def __repr__(self):
        return f"Book('{self.title}', {self.pages})"
    
    def __len__(self):
        return self.pages
    
    def __eq__(self, other):
        return self.title == other.title
    
    def __lt__(self, other):
        return self.pages < other.pages

book = Book("Python Guide", 300)
print(str(book))     # Book: Python Guide
print(len(book))     # 300

🔄 高级特性

装饰器

# 简单装饰器
def timer(func):
    import time
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        end = time.time()
        print(f"{func.__name__} took {end - start:.4f} seconds")
        return result
    return wrapper

@timer
def slow_function():
    import time
    time.sleep(1)
    return "Done"

# 带参数的装饰器
def repeat(times):
    def decorator(func):
        def wrapper(*args, **kwargs):
            for _ in range(times):
                result = func(*args, **kwargs)
            return result
        return wrapper
    return decorator

@repeat(3)
def say_hello():
    print("Hello!")

生成器

# 生成器函数
def fibonacci(n):
    a, b = 0, 1
    for _ in range(n):
        yield a
        a, b = b, a + b

# 使用生成器
for num in fibonacci(10):
    print(num)

# 生成器表达式
squares = (x**2 for x in range(10))
print(list(squares))

上下文管理器

# 使用 with 语句
with open('file.txt', 'r') as f:
    content = f.read()
# 文件自动关闭

# 自定义上下文管理器
class Timer:
    def __enter__(self):
        import time
        self.start = time.time()
        return self
    
    def __exit__(self, exc_type, exc_val, exc_tb):
        import time
        self.end = time.time()
        print(f"Elapsed time: {self.end - self.start:.4f} seconds")

with Timer():
    # 一些耗时操作
    sum(range(1000000))

📁 文件操作

文件读写

# 写文件
with open('data.txt', 'w') as f:
    f.write("Hello, World!\n")
    f.writelines(["Line 1\n", "Line 2\n"])

# 读文件
with open('data.txt', 'r') as f:
    content = f.read()          # 读取全部内容
    
with open('data.txt', 'r') as f:
    lines = f.readlines()       # 读取所有行
    
with open('data.txt', 'r') as f:
    for line in f:              # 逐行读取
        print(line.strip())

# JSON 操作
import json

data = {"name": "Alice", "age": 30}
with open('data.json', 'w') as f:
    json.dump(data, f, indent=2)

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

⚠️ 异常处理

基本异常处理

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")
except Exception as e:
    print(f"An error occurred: {e}")
else:
    print("No exceptions occurred")
finally:
    print("This always executes")

# 抛出异常
def validate_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative")
    if age > 150:
        raise ValueError("Age seems unrealistic")
    return age

📦 模块和包

导入模块

# 标准库
import os
import sys
from datetime import datetime, date
from collections import defaultdict, Counter

# 第三方库
import requests
import numpy as np
import pandas as pd

# 自定义模块
from my_module import my_function
from my_package.my_module import MyClass

创建模块

# my_utils.py
def add(a, b):
    """加法函数"""
    return a + b

def multiply(a, b):
    """乘法函数"""
    return a * b

PI = 3.14159

# 使用模块
import my_utils
result = my_utils.add(5, 3)

🧪 测试

单元测试

import unittest

class TestMathFunctions(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(2, 3), 5)
        self.assertEqual(add(-1, 1), 0)
    
    def test_divide(self):
        self.assertEqual(divide(10, 2), 5)
        with self.assertRaises(ZeroDivisionError):
            divide(10, 0)
    
    def setUp(self):
        # 测试前准备
        self.test_data = [1, 2, 3, 4, 5]
    
    def tearDown(self):
        # 测试后清理
        pass

if __name__ == '__main__':
    unittest.main()

🔍 常用内置函数

# 数学函数
abs(-5)                 # 5 (绝对值)
max(1, 2, 3)           # 3 (最大值)
min(1, 2, 3)           # 1 (最小值)
sum([1, 2, 3])         # 6 (求和)
round(3.14159, 2)      # 3.14 (四舍五入)

# 类型转换
int("123")             # 123
float("3.14")          # 3.14
str(123)               # "123"
list("hello")          # ['h', 'e', 'l', 'l', 'o']
tuple([1, 2, 3])       # (1, 2, 3)

# 序列函数
len([1, 2, 3])         # 3 (长度)
sorted([3, 1, 2])      # [1, 2, 3] (排序)
reversed([1, 2, 3])    # 反向迭代器
enumerate(['a', 'b'])  # [(0, 'a'), (1, 'b')]
zip([1, 2], ['a', 'b']) # [(1, 'a'), (2, 'b')]

# 过滤和映射
filter(lambda x: x > 0, [-1, 0, 1, 2])  # [1, 2]
map(lambda x: x**2, [1, 2, 3])          # [1, 4, 9]
all([True, True, False])                 # False
any([True, False, False])                # True

📚 常用标准库

# 日期时间
from datetime import datetime, date, timedelta
now = datetime.now()
today = date.today()
tomorrow = today + timedelta(days=1)

# 随机数
import random
random.randint(1, 10)          # 1-10之间的随机整数
random.choice(['a', 'b', 'c']) # 随机选择
random.shuffle([1, 2, 3])      # 随机打乱

# 正则表达式
import re
pattern = r'\d+'               # 匹配数字
text = "I have 5 apples and 3 oranges"
numbers = re.findall(pattern, text)  # ['5', '3']

# 系统操作
import os
os.getcwd()                    # 获取当前目录
os.listdir('.')               # 列出目录内容
os.path.exists('file.txt')    # 检查文件是否存在

# HTTP 请求
import requests
response = requests.get('https://api.github.com')
data = response.json()

🎯 最佳实践

代码风格 (PEP 8)

# 好的命名
user_name = "alice"           # 变量用下划线
MAX_SIZE = 100               # 常量用大写
class UserAccount:           # 类名用驼峰命名
    pass

def calculate_total():       # 函数名用下划线
    pass

# 适当的空格和换行
def function(param1, param2):
    """函数文档字符串"""
    if param1 > param2:
        return param1
    else:
        return param2

# 导入顺序
import os                    # 标准库
import sys

import requests             # 第三方库

from my_module import func  # 本地模块

错误处理

# 具体的异常处理
try:
    with open('file.txt', 'r') as f:
        data = f.read()
except FileNotFoundError:
    print("File not found")
except PermissionError:
    print("Permission denied")
except Exception as e:
    print(f"Unexpected error: {e}")

性能优化

# 使用列表推导式而不是循环
# 慢
result = []
for i in range(1000):
    if i % 2 == 0:
        result.append(i**2)

# 快
result = [i**2 for i in range(1000) if i % 2 == 0]

# 使用生成器节省内存
def large_sequence():
    for i in range(1000000):
        yield i**2

# 使用 join 连接字符串
# 慢
result = ""
for word in words:
    result += word + " "

# 快
result = " ".join(words)

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这个快速参考手册涵盖了 Python 编程的核心概念和常用语法。建议收藏并在编程时随时查阅！🐍✨