# 變量的基本賦值
message = "Hello, Python"  # 字符串類型
count = 42                  # 整數(shù)類型
price = 19.99               # 浮點(diǎn)類型
is_valid = True             # 布爾類型

# 變量是對(duì)象的引用
a = [1, 2, 3]  # a 引用了列表對(duì)象
b = a          # b 引用了同一個(gè)列表對(duì)象
b.append(4)    # 修改b指向的列表
print(a)       # 輸出: [1, 2, 3, 4] - a也改變了！
# 驗(yàn)證內(nèi)存地址
print(id(a))   # 輸出內(nèi)存地址
print(id(b))   # 與a相同，證明指向同一對(duì)象

# 變量的類型可以動(dòng)態(tài)改變
x = 10          # x是整數(shù)
print(type(x))  # <class 'int'>
x = "Hello"     # x現(xiàn)在是字符串
print(type(x))  # <class 'str'>
x = [1, 2, 3]   # x現(xiàn)在是列表
print(type(x))  # <class 'list'>

# 多重賦值
a, b, c = 1, 2, 3
print(a, b, c)  # 1 2 3
# 交換變量 - Python特色語(yǔ)法
x, y = 10, 20
x, y = y, x     # 優(yōu)雅地交換
print(x, y)     # 20 10
# 序列解包
numbers = [1, 2, 3]
first, second, third = numbers
print(first)    # 1
# 使用星號(hào)收集剩余元素
first, *rest, last = [1, 2, 3, 4, 5]
print(first)    # 1
print(rest)     # [2, 3, 4]
print(last)     # 5

# LEGB規(guī)則：Local -> Enclosing -> Global -> Built-in
global_var = "全局變量"  # 全局作用域
def outer_function():
    enclosing_var = "嵌套變量"  # 嵌套作用域
    def inner_function():
        local_var = "局部變量"  # 局部作用域
        print(local_var)
        print(enclosing_var)    # 可以訪問(wèn)外層變量
        print(global_var)       # 可以訪問(wèn)全局變量
    inner_function()
outer_function()

# 常量通常用大寫字母命名
MAX_CONNECTIONS = 1000
DEFAULT_TIMEOUT = 30
PI = 3.14159
# 注意：這仍然是變量，可以修改，但不應(yīng)該修改
MAX_CONNECTIONS = 2000  # 技術(shù)上可行，但違反約定

# 不好的命名
a = "張三"
b = 25
c = True
# 好的命名
user_name = "張三"
user_age = 25
is_active = True

# 不好的命名
usr_cnt = 10
txt = "Hello"
val = calculate()
# 好的命名
user_count = 10
message_text = "Hello"
result = calculate()

# 不好的函數(shù)命名
def name():
    return user.name
def data():
    return fetch_data()
# 好的函數(shù)命名
def get_user_name():
    return user.name
def fetch_user_data():
    return fetch_data()

# 布爾變量通常用is/has/can開頭
is_authenticated = True
has_permission = False
can_edit = True
is_visible = False

# 循環(huán)計(jì)數(shù)器
for i in range(10):  # i, j, k 常用于循環(huán)計(jì)數(shù)
    print(i)
# 數(shù)學(xué)公式
for x, y in points:  # x, y 常用于坐標(biāo)
    distance = (x**2 + y**2)**0.5
# 臨時(shí)變量
_, value = get_pair()  # _ 表示我們不關(guān)心的值

class User:
    def __init__(self, name):
        self.name = name           # 公有屬性
        self._internal_id = 123    # 私有屬性（約定）
        self.__password = "secret" # 名稱修飾（避免子類沖突）
    def _internal_method(self):    # 私有方法
        pass
    def __str__(self):             # 魔術(shù)方法
        return self.name
# 訪問(wèn)測(cè)試
user = User("Alice")
print(user.name)           # 可以訪問(wèn)
print(user._internal_id)   # 技術(shù)上可以訪問(wèn)，但不應(yīng)該
# print(user.__password)   # 報(bào)錯(cuò)：屬性不存在
print(user._User__password) # 名稱修飾后的實(shí)際名稱

from typing import List, Optional
# 帶類型注解的變量
name: str = "Alice"
age: int = 30
scores: List[float] = [95.5, 87.0, 92.5]
# 函數(shù)參數(shù)和返回值類型注解
def greet(user_name: str, is_formal: bool = False) -> str:
    """生成問(wèn)候語(yǔ)"""
    prefix = "Dear" if is_formal else "Hello"
    return f"{prefix} {user_name}"
# Optional表示可能為None
def find_user(user_id: int) -> Optional[dict]:
    # 返回用戶字典或None
    pass

# Django框架
class BlogPost(models.Model):
    title = models.CharField(max_length=200)
    publish_date = models.DateTimeField()  # 下劃線命名
    def get_absolute_url(self):  # 特定方法名
        return f"/post/{self.id}/"
# Flask框架
app = Flask(__name__)
@app.route('/users/<int:user_id>')
def get_user_profile(user_id):  # 函數(shù)名明確
    return render_template('profile.html')
# 數(shù)據(jù)科學(xué)（Pandas）
df_users = pd.read_csv('users.csv')  # df_前綴表示DataFrame

# 重構(gòu)前
temp = calculate_average(scores)
if temp > 60:
    print("Pass:", temp)
# 重構(gòu)后 - 使用更有意義的名稱
average_score = calculate_average(scores)
if average_score > 60:
    print("Pass:", average_score)

# 代碼氣味1：魔法數(shù)字
def calculate_price(quantity):
    return quantity * 299  # 299是什么？
# 改進(jìn)
PRODUCT_PRICE = 299
def calculate_price(quantity):
    return quantity * PRODUCT_PRICE
# 代碼氣味2：過(guò)長(zhǎng)參數(shù)列表
def process(name, age, email, phone, address, city, country, zipcode):
    pass
# 改進(jìn)
class UserData:
    def __init__(self, name, age, email, phone, address):
        self.name = name
        # ...
def process(user_data: UserData):
    pass

# 不好的實(shí)現(xiàn)
class user:
    def __init__(self, n, a):
        self.n = n  # name
        self.a = a  # age
        self.s = True  # status
    def g_n(self):
        return self.n
# 好的實(shí)現(xiàn)
class User:
    """用戶類"""
    def __init__(self, name: str, age: int):
        self.name = name
        self.age = age
        self.is_active = True  # 狀態(tài)名清晰
    def get_name(self) -> str:
        """獲取用戶名"""
        return self.name
    def deactivate(self):
        """停用用戶"""
        self.is_active = False

class ShoppingCart:
    def __init__(self):
        self._items = []  # 私有屬性
        self.total_price = 0.0
    def add_item(self, item_name: str, price: float, quantity: int = 1):
        """添加商品到購(gòu)物車"""
        for _ in range(quantity):
            self._items.append(item_name)
        self.total_price += price * quantity
    def get_item_count(self) -> int:
        """獲取商品總數(shù)"""
        return len(self._items)
    def is_empty(self) -> bool:
        """判斷購(gòu)物車是否為空"""
        return len(self._items) == 0
# 使用示例
cart = ShoppingCart()
cart.add_item("Python編程", 89.00, 2)
cart.add_item("機(jī)械鍵盤", 299.00)
if not cart.is_empty():
    print(f"購(gòu)物車共{cart.get_item_count()}件商品")
    print(f"總價(jià): ￥{cart.total_price}")

# pylint - 檢查命名規(guī)范
pip install pylint
pylint your_script.py
# flake8 - 綜合檢查
pip install flake8
flake8 your_script.py
# black - 自動(dòng)格式化
pip install black
black your_script.py