# 示例：应收账款(Accounts Receivable)逾期天数与风险标签
days_past_due = 75  # 逾期天数

is_overdue = days_past_due > 0 # 请注意，这里的比较运算符是 `>`，而不是赋值运算符 `=`
is_high_risk = days_past_due >= 90
is_medium_risk = (days_past_due >= 60) and (days_past_due < 90)
is_medium_risk = (90 > days_past_due >= 60)  # 也可以这样写，效果一样

print("is_overdue:", is_overdue)
print("is_high_risk:", is_high_risk)
print("is_medium_risk:", is_medium_risk)

# 示例：用“真值规则”判断是否有数据
transactions = []   # 空列表 => False
if transactions:
    print("有交易数据，需要汇总。")
else:
    print("没有交易数据，跳过汇总。")

note = ""  # 空字符串 => False
if not note:
    print("备注为空。")

if 条件1:
    代码块1
elif 条件2:
    代码块2
else:
    代码块3

# 示例：应收账款逾期分层（aging bucket）
days_past_due = 120

if days_past_due <= 0:
    bucket = "未逾期"
elif days_past_due <= 30:
    bucket = "1-30天"
elif days_past_due <= 60:
    bucket = "31-60天"
elif days_past_due <= 90:
    bucket = "61-90天"
else:
    bucket = "90天以上"

print("逾期天数:", days_past_due, "=> 分层:", bucket)


# if语句可以没有else部分
score = 85
if score >= 60:
    print("及格")

# if-elif语句也可以没有else部分
score = 85
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
elif score >= 60:
    grade = "D"
print("分数:", score, "=> 等级:", grade)

# 示例：先判断是否逾期，再判断金额是否需要计提
days_past_due = 35
amount = 180  # 金额（元）

if days_past_due > 0:
    # 已逾期
    if amount >= 200:
        action = "需要关注并计提/催收"
    else:
        action = "已逾期，但金额较小，记录即可"
else:
    action = "未逾期"

print(action)

结果 = A if 条件 else B

# 示例：根据利润正负给出标签
profit = -12.5

# if profit >=0:
#     label = '盈利'
# else:
#     label = '亏损'
# print(profit, label)
# 以上四行代码与以下两行代码起到完全一模一样的效果

label = "盈利" if profit >= 0 else "亏损"
print(profit, label)

category = 'travel'
amount = 3200

if category == 'travel' and amount > 3000:
    print('需要主管审批')
elif category == 'meal' and amount >500:
    print('需要说明')
else:
    print('正常')

需要主管审批

# 遍历列表：逐个访问元素
amounts = [120.0, 88.5, 230.0]  # 一组金额

for x in amounts:
    print(x)

amounts = [120.0, 88.5, 230.0]  # 一组金额
x = amounts[0]
print(x)
x = amounts[1]
print(x)
x = amounts[2]
print(x)
print('循环结束。')

# 但是这种方法在列表更新后无法自动更新遍历内容。相比之下，for循环的功能更加强大，可以随列表的变化进行实时更新。

120.0
88.5
230.0
循环结束。

amounts = [120.0, 88.5, 230.0]  # 一组金额

for x in amounts:
    x += 1
    print(x)

121.0
89.5
231.0

# 遍历元组：逐个访问元素
t = ("Sales", "COGS", "Rent")

for x in t:
    print(x)

# 示例字典
d = {"Sales": 1700.50, "COGS": 630.20, "Rent": 15000.00}

# 1) 遍历键（默认就是键）
for k in d:
    print("key =", k)

print("---")

# 也可以写得更明确：遍历键
for k in d.keys():
    print("key =", k)

print("---")

# 2) 遍历值
for v in d.values():
    print("value =", v)

print("---")

# 3) 同时遍历键和值（最常用）
for k, v in d.items():
    print(k, "->", v)

# 遍历集合（了解）：集合是无序的，遍历顺序不保证一致
s = {"b", "a", "c"}

for x in s:
    print(x)

print("sorted iteration:")
for x in sorted(s):   # sorted(...) 返回排好序的列表，顺序稳定
    print(x)

for 变量 in 可迭代对象:
    循环体（重复执行）

# 示例 1：批量汇总交易金额（收入为正，支出为负）
transactions = [100, -20, 300, -50]  
total = 0

for x in transactions:
    total += x  # 逐笔累加

print("总额 total =", total)

transactions = [120, -30, 60, 80, -10, -50, 200, -40]

inflows = []
outflows = []

for amt in transactions:
    if amt >= 0:
        inflows.append(amt)
    else:
        outflows.append(amt)

print("inflows =", inflows)
print("outflows =", outflows)
print("净额 net =", sum(inflows) + sum(outflows))

tx = [1000, -200, -150, 500, -120]
balance = 0
balance_curve = []

for amt in tx:
    balance += amt
    balance_curve.append(balance)

print("balance_curve =", balance_curve)

list(range(5)), list(range(2, 8)), list(range(1, 10, 2))

total = 0
for i in range(1, 101): 
    total += i
print("1~100 总和 =", total)

for idx, value in enumerate(iterable, start=1):
    ...

accounts = ["Cash", "A/R", "Inventory"]
amounts  = [5000, 12000, 8000]

for acc, amt in zip(accounts, amounts):
    print(acc, "=>", amt)

records = [
    {"dept": "Sales", "amount": 1200},
    {"dept": "Sales", "amount": 800},
    {"dept": "R&D",  "amount": 2000},
    {"dept": "HR",   "amount": 500},
    {"dept": "R&D",  "amount": 700},
]

dept_sum = {}

for r in records:
    dept = r["dept"]
    amt = r["amount"]
    dept_sum[dept] = dept_sum.get(dept, 0) + amt

print("dept_sum =", dept_sum)

# 示例：在列表中“找到第一个奇数”就停止（break）
nums = [2, 4, 6, 9, 10, 17]      # 一组数字

for x in nums:               # 逐个遍历 nums
    if x % 2 == 1:           # 判断 x 是否为奇数（除以 2 余 1）
        print("找到奇数：", x)  # 找到后输出
        break                # 立刻退出循环（不再继续往后找）

# 示例：跳过缺失值，汇总有效金额
amounts = [100, "N/A", 200, None, 50]

total = 0
for x in amounts:
    if (x is None) or (x == "N/A"):
        continue
    total += x

print("total =", total)

# 示例：for-else（查找是否存在负数余额）
balances = [120, 80, 50, 0, 30]

for b in balances:
    if b < 0:
        print("发现负数余额：", b)
        break
else:
    print("未发现负数余额")

# 假设已有 12 个月现金流列表

cash_flows = [1200, -300, 500, -800, 0, 600, -200, 100, -50, 900, -400, 700]



total_cf = 0        # 全年累计现金流

n_positive = 0      # 现金流为正的月份个数

while 条件:
    循环体

cash = 1000 # 初始现金余额
monthly_payment = 230 # 每月支付金额
month = 0 # 定义初始值，记录循环的次数

while cash >= monthly_payment:
    cash -= monthly_payment
    month += 1 # 每次循环都要记得更新 month 的值，否则会死循环

print("可支付月数 =", month)
print("最后余额 =", cash)

cost = 120000
salvage = 20000
life_months = 60

monthly_dep = (cost - salvage) / life_months
book_value = cost
m = 0

while book_value - monthly_dep >= salvage:
    book_value -= monthly_dep
    m += 1

print("已计提月数 =", m)
print("期末账面价值 =", round(book_value, 2))

balance = 10000
monthly_rate = 0.01   # 月利率 1%
payment = 300         # 每月固定还款
month = 0
max_months = 600

while (balance > 0) and (month < max_months):
    interest = balance * monthly_rate
    balance = balance + interest - payment
    month += 1
    if balance <= 0:
        balance = 0
        break

print("已还月数 =", month)
print("剩余余额 =", round(balance, 2))
if month == max_months:
    print("提示：达到 max_months，说明还款额可能过小或需要调整参数。")

while True:
    s = input("请输入金额，输入 q 退出：")
    if s == "q":
        break
    amt = float(s)
    print("你输入的金额是：", amt)

stock = 120

sales = [15, 20, 10, 25, 30, 40]   # 每周销量（不固定）

# 示例：把字符串金额转成 float，并捕获 ValueError
raw_amount = "12.5a"

try:
    amt = float(raw_amount)
    print("转换成功：", amt)
except ValueError:
    print("转换失败：raw_amount =", raw_amount)

raw_amounts = ["100", "20.5", "N/A", "", None, "30"]
valid = []
invalid = []

for x in raw_amounts:
    try:
        amt = float(x)
        valid.append(amt)
    except (ValueError, TypeError):
        invalid.append(x)

print("valid:", valid)
print("invalid:", invalid)
print("sum(valid) =", sum(valid))

def safe_margin(profit, revenue):
    """安全计算利润率：遇到分母为0则返回 None"""
    try:
        return profit / revenue
    except ZeroDivisionError:
        return None

print(safe_margin(10, 100))
print(safe_margin(10, 0))

raw = "88"

try:
    x = int(raw)
except ValueError:
    print("raw 不是整数")
else:
    print("转换成功，x =", x)
finally:
    print("finally：这句一定会执行")

items = [10, 5, 0, 2]

for x in items:
    try:
        print("处理 x =", x)
        if x == 0:
            print("遇到关键值：停止处理")
            break
        y = 100 / x
        print("结果 y =", y)
    finally:
        # 真实业务里这里可能是：写进度日志、关闭资源、提交/回滚等
        print("finally：完成本轮收尾")

第 3 章 流程控制¶

3.0 课前导入与学习路线¶

本章学习目标¶

3.1 条件语句（Conditional Statements）¶

3.1.1 比较运算符和逻辑运算符¶

3.1.2 “真值”规则（Truthiness）¶

3.1.3 if / elif / else 结构¶

3.1.4 嵌套判断（Nested if）¶

3.1.5 条件表达式（Conditional Expression）¶

练习 3-1：费用报销规则判断¶

3.2 循环与遍历（Loops & Iteration）¶

3.2.1 可迭代对象（Iterable）是什么？¶

3.2.2 常见容器的遍历¶

3.2.2.1 遍历列表¶

3.2.2.2 遍历元组¶

3.2.2.3 遍历字典 dict：keys / values / items¶

3.2.2.4 遍历集合（了解）¶

3.2.3 for 循环¶

例题：把交易分成“流入/流出”（构建新列表）¶

例题：生成“累计余额曲线”（running balance）¶

3.2.3.1 range：生成整数序列（常用于“固定次数”）¶

示例：计算 1 到 100 的自然数总和（for + range）¶

3.2.3.2 enumerate：同时拿到索引和元素¶

3.2.3.3 zip：并行遍历多个序列当两列数据需要“一一对应”处理时，用 zip 很方便（例如：科目名和金额一一对应）。¶

例题：部门报销汇总（用 dict 累加）¶

3.2.3.4 break / continue / for-else：控制循环¶

for 的执行顺序¶

练习 3-2：用 for 计算 12 个月累计现金流¶

3.2.4 while 循环¶

例题：现金余额逐月扣减，直到不足以支付（while）¶

例题：按月计提折旧，直到达到残值（while）¶

例题：贷款余额逐月计息并还款（while + 最大迭代次数）¶

while + break：输入控制（模板）¶

while 的执行顺序¶

练习 3-3：用 while 模拟“库存清零”¶

3.2.5 for vs while：怎么选？¶

3.3 异常处理语句（Exception Handling）¶

3.3.1 最常见的几类错误¶

3.3.2 批量处理中最常见的写法：循环 + try/except¶

3.3.3 捕获“具体异常” vs 捕获“所有异常”¶

3.3.4 try/except/else/finally¶

finally 在循环中的常见用法：每轮处理都做“收尾动作”¶

练习 3-4：批量计算“单笔税额”，并记录问题行¶

3.4 本章小结与自测¶

小结（你现在应该会）¶

快速自测¶

第 3 章流程控制¶

3.2.3.3 zip：并行遍历多个序列当两列数据需要“一一对应”处理时，用 `zip` 很方便（例如：科目名和金额一一对应）。¶