Hello World与基础练习

动手写代码，巩固基础知识

第一个程序

Hello World

# hello.py
print("Hello, World!")
print("你好，世界！")
print("开始我的编程之旅！")

运行：

python hello.py

为什么是Hello World

• 编程界的传统（源于1978年《C程序设计语言》）
• 验证环境配置正确
• 最简单的起点

---

基础练习题

练习1：个人信息

# 输出你的个人信息
name = "你的名字"
age = 20
city = "你的城市"
hobby = "你的爱好"

print(f"大家好，我是{name}")
print(f"今年{age}岁，来自{city}")
print(f"我的爱好是{hobby}")

练习2：简单计算

# 计算两个数的和、差、积、商
a = 15
b = 4

print(f"{a} + {b} = {a + b}")
print(f"{a} - {b} = {a - b}")
print(f"{a} × {b} = {a * b}")
print(f"{a} ÷ {b} = {a / b:.2f}")
print(f"{a} 整除 {b} = {a // b}")
print(f"{a} 取余 {b} = {a % b}")

练习3：用户输入

# 获取用户输入并问候
name = input("请输入你的名字：")
print(f"你好，{name}！欢迎学习Python！")

练习4：温度转换

# 摄氏度转华氏度
celsius = float(input("请输入摄氏温度："))
fahrenheit = celsius * 9/5 + 32
print(f"{celsius}°C = {fahrenheit}°F")

练习5：判断奇偶

# 判断一个数是奇数还是偶数
num = int(input("请输入一个整数："))

if num % 2 == 0:
    print(f"{num}是偶数")
else:
    print(f"{num}是奇数")

---

条件判断练习

练习6：成绩等级

score = int(input("请输入分数(0-100)："))

if score >= 90:
    grade = "优秀 A"
elif score >= 80:
    grade = "良好 B"
elif score >= 70:
    grade = "中等 C"
elif score >= 60:
    grade = "及格 D"
else:
    grade = "不及格 F"

print(f"成绩等级：{grade}")

练习7：闰年判断

year = int(input("请输入年份："))

if (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0):
    print(f"{year}年是闰年")
else:
    print(f"{year}年不是闰年")

练习8：三角形判断

a = float(input("边a："))
b = float(input("边b："))
c = float(input("边c："))

if a + b > c and a + c > b and b + c > a:
    print("可以构成三角形")
    if a == b == c:
        print("这是等边三角形")
    elif a == b or b == c or a == c:
        print("这是等腰三角形")
    else:
        print("这是普通三角形")
else:
    print("不能构成三角形")

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循环练习

练习9：九九乘法表

for i in range(1, 10):
    for j in range(1, i + 1):
        print(f"{j}×{i}={i*j}", end="\t")
    print()

输出：

1×1=1
1×2=2   2×2=4
1×3=3   2×3=6   3×3=9
...

练习10：求和

# 计算1到100的和
total = 0
for i in range(1, 101):
    total += i
print(f"1到100的和是：{total}")  # 5050

# 一行代码
print(sum(range(1, 101)))

练习11：阶乘

n = int(input("请输入n："))
factorial = 1

for i in range(1, n + 1):
    factorial *= i

print(f"{n}! = {factorial}")

练习12：斐波那契数列

n = int(input("输出前n个斐波那契数："))

a, b = 0, 1
for _ in range(n):
    print(a, end=" ")
    a, b = b, a + b
print()

练习13：打印图形

# 直角三角形
n = 5
for i in range(1, n + 1):
    print("*" * i)

# 倒三角
for i in range(n, 0, -1):
    print("*" * i)

# 金字塔
for i in range(1, n + 1):
    print(" " * (n - i) + "*" * (2 * i - 1))

---

函数练习

练习14：判断质数

def is_prime(n):
    """判断是否为质数"""
    if n < 2:
        return False
    for i in range(2, int(n**0.5) + 1):
        if n % i == 0:
            return False
    return True

# 测试
for i in range(1, 20):
    if is_prime(i):
        print(i, end=" ")
# 2 3 5 7 11 13 17 19

练习15：最大公约数

def gcd(a, b):
    """求最大公约数（辗转相除法）"""
    while b:
        a, b = b, a % b
    return a

print(gcd(48, 18))  # 6

练习16：回文判断

def is_palindrome(s):
    """判断是否为回文"""
    s = s.lower().replace(" ", "")
    return s == s[::-1]

print(is_palindrome("level"))  # True
print(is_palindrome("hello"))  # False
print(is_palindrome("A man a plan a canal Panama"))  # True

---

列表练习

练习17：列表操作

# 创建学生成绩列表
scores = [85, 92, 78, 95, 88, 76, 90]

# 统计
print(f"总人数：{len(scores)}")
print(f"最高分：{max(scores)}")
print(f"最低分：{min(scores)}")
print(f"平均分：{sum(scores)/len(scores):.2f}")

# 排序
sorted_scores = sorted(scores, reverse=True)
print(f"排名：{sorted_scores}")

# 筛选及格
passed = [s for s in scores if s >= 60]
print(f"及格人数：{len(passed)}")

练习18：去重排序

numbers = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]

# 去重并排序
unique_sorted = sorted(set(numbers))
print(unique_sorted)  # [1, 2, 3, 4, 5, 6, 9]

---

字典练习

练习19：词频统计

text = "apple banana apple cherry banana apple"
words = text.split()

# 统计词频
word_count = {}
for word in words:
    word_count[word] = word_count.get(word, 0) + 1

print(word_count)  # {'apple': 3, 'banana': 2, 'cherry': 1}

# 或用Counter
from collections import Counter
print(Counter(words))

练习20：学生管理

students = {
    "001": {"name": "张三", "score": 85},
    "002": {"name": "李四", "score": 92},
    "003": {"name": "王五", "score": 78}
}

# 遍历
for sid, info in students.items():
    print(f"{sid}: {info['name']} - {info['score']}分")

# 找最高分
top = max(students.items(), key=lambda x: x[1]["score"])
print(f"最高分：{top[1]['name']}")

---

综合练习

练习21：石头剪刀布

import random

choices = ["石头", "剪刀", "布"]

while True:
    user = input("请出拳（石头/剪刀/布）或输入q退出：")
    if user == "q":
        break
    if user not in choices:
        print("无效输入")
        continue

    computer = random.choice(choices)
    print(f"电脑出：{computer}")

    if user == computer:
        print("平局！")
    elif (user == "石头" and computer == "剪刀") or \
         (user == "剪刀" and computer == "布") or \
         (user == "布" and computer == "石头"):
        print("你赢了！")
    else:
        print("你输了！")

练习22：简单通讯录

contacts = {}

while True:
    print("\n===== 通讯录 =====")
    print("1. 添加联系人")
    print("2. 查找联系人")
    print("3. 显示所有")
    print("4. 删除联系人")
    print("5. 退出")

    choice = input("请选择：")

    if choice == "1":
        name = input("姓名：")
        phone = input("电话：")
        contacts[name] = phone
        print("添加成功！")
    elif choice == "2":
        name = input("输入姓名：")
        if name in contacts:
            print(f"{name}: {contacts[name]}")
        else:
            print("未找到")
    elif choice == "3":
        for name, phone in contacts.items():
            print(f"{name}: {phone}")
    elif choice == "4":
        name = input("输入姓名：")
        if name in contacts:
            del contacts[name]
            print("删除成功！")
        else:
            print("未找到")
    elif choice == "5":
        print("再见！")
        break

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本章小结

通过这些练习，你应该掌握了：

1. 基础语法：变量、输入输出、运算符
2. 条件判断：if-elif-else
3. 循环：for、while
4. 函数：定义和调用
5. 数据结构：列表、字典
6. 综合应用：小程序开发

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下一步

做完基础练习，下一章开发一个完整的计算器项目。

→ 继续阅读：26-计算器项目实战