Python 10 分钟极速上手手册：从零开始写出你的第一行代码

brew install python
python3 --version

sudo apt install python3 python3-pip
python3 --version

print("Hello, World!")

python3 hello.py
# 输出: Hello, World!

print("你好，Python！")
print(42)              # 数字不需要引号
print(3.14)
print(True)            # 布尔值

name = "Alice"        # str 字符串
age = 25              # int 整数
height = 1.68         # float 浮点数
is_student = True     # bool 布尔值（真/假）
hobbies = None        # NoneType 空值

print(type(name))     # <class 'str'>
print(type(age))      # <class 'int'>
print(type(height))   # <class 'float'>

a = 10
b = 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（总是返回 float）
print(a // b)   # 3    整除（向下取整）
print(a % b)    # 1    取余
print(a ** b)   # 1000 幂运算

print(5 == 5)     # True   等于
print(5 != 3)     # True   不等于
print(5 > 3)      # True   大于
print(5 <= 3)     # False  小于等于

print(True and False)  # False
print(True or False)   # True
print(not True)        # False
print(5 > 3 and 7 < 10)   # True

# 三种创建方式
greeting = "Hello"
name = 'Alice'
message = """这是一个
多行字符串"""

# 拼接
full_greeting = greeting + ", " + name
print(full_greeting)   # Hello, Alice

# f-string（推荐）—— 最优雅的字符串格式化
greeting = f"你好，{name}！你今年{age}岁。"
print(greeting)   # 你好，Alice！你今年25岁。

text = "  Hello, Python!  "

print(text.strip())            # "Hello, Python!"  去除首尾空格
print(text.lower())            # "  hello, python!  "
print(text.upper())            # "  HELLO, PYTHON!  "
print(text.replace("Hello", "Hi"))   # "  Hi, Python!  "
print(text.split(", "))        # ['  Hello', 'Python!  ']
print("Python" in text)        # True
print(len(text))               # 18

s = "Python"

print(s[0])      # P   第一个字符
print(s[-1])     # n   最后一个字符
print(s[0:3])    # Pyt  索引 0 到 2
print(s[:3])     # Pyt  从开始到索引 2
print(s[3:])     # hon  从索引 3 到末尾
print(s[::2])    # Pto  每隔一个字符取一个
print(s[::-1])   # nohtyP  反转字符串

score = 85

if score >= 90:
    grade = "A"
    print("优秀！")
elif score >= 80:
    grade = "B"
    print("良好！")
elif score >= 70:
    grade = "C"
    print("中等")
else:
    grade = "D"
    print("需要加油")

print(f"等级: {grade}")

result = "及格" if score >= 60 else "不及格"
print(result)

# 遍历列表
fruits = ["苹果", "香蕉", "橙子"]
for fruit in fruits:
    print(f"我喜欢吃{fruit}")

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

# enumerate：同时获取索引和值
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

count = 0
while count < 5:
    print(f"计数: {count}")
    count += 1   # 等价于 count = count + 1

# break：立即退出循环
for i in range(10):
    if i == 5:
        break
    print(i)   # 0, 1, 2, 3, 4

# continue：跳过当前迭代
for i in range(5):
    if i == 2:
        continue
    print(i)   # 0, 1, 3, 4

# 传统写法
squares = []
for x in range(10):
    squares.append(x ** 2)

# 列表推导式（更简洁）
squares = [x ** 2 for x in range(10)]
tens = [x for x in range(20) if x % 2 == 0]  # 偶数列表
print(tens)   # [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

# 创建列表
numbers = [1, 2, 3, 4, 5]
mixed = [1, "hello", 3.14, True]   # Python 列表可以混合类型
students = ["Alice", "Bob", "Charlie"]

# 基本操作
print(len(students))        # 3
print(students[0])          # Alice
print(students[-1])         # Charlie（最后一个）

# 修改
students[0] = "Anna"        # 修改
students.append("David")    # 末尾添加
students.insert(1, "Ben")   # 在索引 1 插入
students.remove("Bob")      # 移除第一个匹配的元素

# 切片
print(students[1:3])        # ['Ben', 'Charlie']

# 排序
scores = [85, 92, 78, 90]
scores.sort()
print(scores)               # [78, 85, 90, 92]
scores.sort(reverse=True)
print(scores)               # [92, 90, 85, 78]

# 常用内置函数调用
print(sum(scores))          # 345
print(max(scores))          # 92
print(min(scores))          # 78

# 创建字典
user = {
    "name": "Alice",
    "age": 25,
    "email": "alice@example.com",
    "is_active": True
}

# 访问
print(user["name"])          # Alice
print(user.get("phone", "未设置"))   # 未设置（安全访问，不存在时返回默认值）

# 修改与添加
user["age"] = 26
user["phone"] = "13800138000"

# 遍历
def show_dict(d):
    for key, value in d.items():
        print(f"{key}: {value}")

show_dict(user)

# 删除
print(user.pop("phone", None))  # 删除并返回值

def greet(name):
    """向某人打招呼"""
    return f"你好, {name}!"

# 调用
message = greet("Alice")
print(message)

def calculate_area(width, height=10):
    """计算矩形面积，高度默认 10"""
    return width * height

print(calculate_area(5))        # 50（高默认 10）
print(calculate_area(5, 8))     # 40
print(calculate_area(height=8, width=5))   # 40（关键字参数）

def sum_all(*numbers):
    """接受任意数量的数字并求和"""
    total = 0
    for n in numbers:
        total += n
    return total

print(sum_all(1, 2, 3, 4))    # 10

# 等价于 def square(x): return x ** 2
square = lambda x: x ** 2

print(square(5))   # 25

# 常用场景：配合排序
users = [("Alice", 25), ("Bob", 20), ("Charlie", 30)]
users.sort(key=lambda x: x[1])   # 按年龄排序
print(users)   # [('Bob', 20), ('Alice', 25), ('Charlie', 30)]

# 写入文件（自动关闭）
with open("greeting.txt", "w", encoding="utf-8") as f:
    f.write("Hello, Python!\n")
    f.write("第二行内容\n")

# 读取文件
with open("greeting.txt", "r", encoding="utf-8") as f:
    content = f.read()
    print(content)

# 逐行读取
with open("greeting.txt", "r", encoding="utf-8") as f:
    for line in f:
        print(line.strip())

from pathlib import Path

# 路径操作
p = Path("data/users.txt")
p.write_text("Alice, 25\nBob, 30\n", encoding="utf-8")

content = p.read_text(encoding="utf-8")
print(content)

# 检查文件存在
if p.exists():
    print(f"{p} 存在，大小: {p.stat().st_size} 字节")

def safe_divide(a, b):
    """安全除法，处理除零错误"""
    try:
        result = a / b
        return result
    except ZeroDivisionError:
        return "错误：除数不能为零"
    except TypeError:
        return "错误：请输入数字"
    except Exception as e:
        return f"未知错误: {e}"
    finally:
        print("计算完成")

# 测试
print(safe_divide(10, 2))       # 5.0
print(safe_divide(10, 0))       # 错误：除数不能为零
print(safe_divide("a", 2))      # 错误：请输入数字

import json

def load_weather_data():
    """加载天气数据（模拟从文件读取）"""
    # 实际项目中这里会调用 API，如 requests.get(url)
    return {
        "北京": {"temp": 25, "condition": "晴", "humidity": 45},
        "上海": {"temp": 28, "condition": "多云", "humidity": 60},
        "广州": {"temp": 32, "condition": "雷阵雨", "humidity": 80},
    }

def check_weather(city, weather_data):
    """查询指定城市的天气"""
    if city in weather_data:
        data = weather_data[city]
        return (f"🌤 {city} 天气\n"
                f"温度: {data['temp']}°C\n"
                f"天气: {data['condition']}\n"
                f"湿度: {data['humidity']}%")
    else:
        return f"抱歉，暂无 {city} 的天气信息。"

def main():
    """主程序"""
    weather_data = load_weather_data()
    
    print("欢迎使用天气查询助手！")
    print("支持城市：北京、上海、广州")
    print("输入 'quit' 退出\n")
    
    while True:
        city = input("请输入城市名: ").strip()
        
        if city.lower() == "quit":
            print("再见！")
            break
        
        if city:
            print(check_weather(city, weather_data))
            print()

if __name__ == "__main__":
    main()