以此文件编写信息系统代码

根据提供的《系统分析报告.doc》，以下是使用Python和SQLite编写的宠物体重管理系统的简化版本代码示例。此示例实现了用户注册、登录、添加宠物、记录体重和查询体重历史等功能。

### 环境准备
首先，确保安装了 `sqlite3` 模块（通常 Python 自带）。

### 数据库初始化

import sqlite3
from datetime import datetime, timedelta

def init_db():
    conn = sqlite3.connect('pet_weight.db')
    c = conn.cursor()
    
    # 创建用户表
    c.execute('''CREATE TABLE IF NOT EXISTS users (
                    id INTEGER PRIMARY KEY,
                    username TEXT UNIQUE,
                    password TEXT
                )''')
    
    # 创建宠物表
    c.execute('''CREATE TABLE IF NOT EXISTS pets (
                    id INTEGER PRIMARY KEY,
                    user_id INTEGER,
                    pet_name TEXT,
                    FOREIGN KEY(user_id) REFERENCES users(id)
                )''')
    
    # 创建宠物体重记录表
    c.execute('''CREATE TABLE IF NOT EXISTS pet_weights (
                    id INTEGER PRIMARY KEY,
                    pet_id INTEGER,
                    weight REAL,
                    recorded_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
                    FOREIGN KEY(pet_id) REFERENCES pets(id)
                )''')
    
    conn.commit()
    conn.close()

init_db()

### 用户注册

def register_user(username, password):
    conn = sqlite3.connect('pet_weight.db')
    c = conn.cursor()
    
    try:
        c.execute("INSERT INTO users (username, password) VALUES (?, ?)", (username, password))
        conn.commit()
        print(f"User {username} registered successfully.")
    except sqlite3.IntegrityError:
        print(f"Username {username} already exists.")
    
    conn.close()

### 用户登录

def login_user(username, password):
    conn = sqlite3.connect('pet_weight.db')
    c = conn.cursor()
    
    c.execute("SELECT * FROM users WHERE username=? AND password=?", (username, password))
    user = c.fetchone()
    
    if user:
        print(f"Welcome, {username}!")
        return True
    else:
        print("Invalid username or password.")
        return False
    
    conn.close()

### 添加宠物

def add_pet(user_id, pet_name):
    conn = sqlite3.connect('pet_weight.db')
    c = conn.cursor()
    
    c.execute("INSERT INTO pets (user_id, pet_name) VALUES (?, ?)", (user_id, pet_name))
    conn.commit()
    print(f"Pet {pet_name} added successfully.")
    
    conn.close()

### 记录宠物体重

def record_weight(pet_id, weight):
    conn = sqlite3.connect('pet_weight.db')
    c = conn.cursor()
    
    c.execute("INSERT INTO pet_weights (pet_id, weight) VALUES (?, ?)", (pet_id, weight))
    conn.commit()
    print(f"Weight for pet ID {pet_id} recorded successfully.")
    
    conn.close()

### 查询宠物体重历史

def get_weight_history(pet_id):
    conn = sqlite3.connect('pet_weight.db')
    c = conn.cursor()
    
    c.execute("SELECT weight, recorded_at FROM pet_weights WHERE pet_id=? ORDER BY recorded_at", (pet_id,))
    history = c.fetchall()
    
    if history:
        print(f"Weight history for pet ID {pet_id}:")
        for weight, recorded_at in history:
            print(f"Weight: {weight}, Recorded at: {recorded_at}")
    else:
        print(f"No weight records found for pet ID {pet_id}.")
    
    conn.close()

### 主程序

def main():
    while True:
        print("\n1. Register\n2. Login\n3. Add Pet\n4. Record Weight\n5. Get Weight History\n6. Exit")
        choice = input("Choose an option: ")
        
        if choice == '1':
            username = input("Enter username: ")
            password = input("Enter password: ")
            register_user(username, password)
        
        elif choice == '2':
            username = input("Enter username: ")
            password = input("Enter password: ")
            if login_user(username, password):
                user_id = get_user_id(username)
                print(f"Logged in as user ID: {user_id}")
        
        elif choice == '3':
            user_id = int(input("Enter your user ID: "))
            pet_name = input("Enter pet name: ")
            add_pet(user_id, pet_name)
        
        elif choice == '4':
            pet_id = int(input("Enter pet ID: "))
            weight = float(input("Enter weight: "))
            record_weight(pet_id, weight)
        
        elif choice == '5':
            pet_id = int(input("Enter pet ID: "))
            get_weight_history(pet_id)
        
        elif choice == '6':
            break
        
        else:
            print("Invalid choice. Please try again.")

if __name__ == "__main__":
    main()

### 辅助函数

def get_user_id(username):
    conn = sqlite3.connect('pet_weight.db')
    c = conn.cursor()
    
    c.execute("SELECT id FROM users WHERE username=?", (username,))
    user_id = c.fetchone()[0]
    
    conn.close()
    return user_id

这个示例代码涵盖了系统的基本功能，并且可以根据需要进一步扩展和完善。希望这对你有帮助！