Python 基础：函数与模块

3.1 函数定义

# 基本函数
def greet(name):
    """打招呼函数"""
    return f"Hello, {name}!"

# 默认参数
def greet(name, greeting="Hello"):
    return f"{greeting}, {name}!"

print(greet("Alice"))              # Hello, Alice!
print(greet("Bob", "Hi"))         # Hi, Bob!

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

print(sum_all(1, 2, 3, 4, 5))   # 15

# 关键字参数
def person_info(name, age, city):
    return f"{name}, {age}岁, 住在{city}"

print(person_info(age=25, name="Alice", city="Beijing"))  # 关键字参数顺序无关

3.2 Lambda 表达式

# lambda 匿名函数
square = lambda x: x ** 2
print(square(5))  # 25

# 配合内置函数使用
numbers = [3, 1, 4, 1, 5, 9, 2]
sorted_nums = sorted(numbers, reverse=True)
print(sorted_nums)  # [9, 5, 4, 3, 2, 1, 1]

# 按绝对值排序
nums = [-5, 3, -2, 8]
sorted_nums = sorted(nums, key=abs)
print(sorted_nums)  # [-2, 3, -5, 8]

3.3 模块导入

# 标准导入
import math
print(math.sqrt(16))  # 4.0

# 指定别名
import numpy as np
import pandas as pd

# 从模块导入特定内容
from datetime import datetime, timedelta
from pathlib import Path

# 导入并起别名
from requests import get as http_get

3.4 模块创建

# mymodule.py
def add(a, b):
    return a + b

PI = 3.14159

# __all__ 控制 from module import * 的导出内容
__all__ = ['add', 'PI']

# main.py
from mymodule import add, PI
print(add(1, 2))      # 3
print(PI)             # 3.14159

3.5 包

mypackage/
├── __init__.py      # 包初始化
├── module1.py
├── module2.py
└── subpackage/
    ├── __init__.py
    └── module3.py

# 导入
from mypackage import module1
from mypackage.subpackage import module3

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