Question

我正在创建一个程序，将项目与code，price和quantity以及 pickle 模块一起保存。

当有人想购物时，他们会输入code。我正在尝试检查文本文档以查看是否保存了code，但它似乎不起作用并且给了我这个错误：

TypeError：“NoneType”类型的参数不可迭代。

有人可以帮忙吗？

stock = readfile()
print("Please enter the GTIN-8 code of the items you want to buy, when you are done type DONE")
while True:
    code = input("Enter GTIN-8 code or DONE ")
    if code == "DONE":
        break
    else:
        amount = int(input("How many would you like? "))

if code in stock:
    print("Yes")
else:
    print("No")

Answer 1

stock函数将None变量设置为readfile。问题可能出在该函数中（可能它实际上并没有打开文件？）。

Answer 2

尝试使用readlines（）：

def readlines():
    return [line.strip() for line in open('fruit.txt','r').readlines()]

Answer 3

仅仅为了变化，这里是使用sqlite3的替代版本。

（注意：钱被视为整数美分。）

import sqlite3

DATABASE = 'stock.db'

def get_int(prompt):
    while True:
        try:
            return int(input(prompt))
        except ValueError:
            pass

def money_str(price, min_width=6):
    return "$ {1:{0:d}d}.{2:02d}".format(min_width - 5, price // 100, price % 100)

def make_stock_table(conn):
    conn.execute("DROP TABLE IF EXISTS Stock;")
    conn.execute(
        """
        CREATE TABLE Stock (
            code     INTEGER  PRIMARY KEY NOT NULL,
            name     TEXT     NOT NULL,
            price    INTEGER  NOT NULL,
            quantity INTEGER  NOT NULL  DEFAULT (0)
        );
        """
    )
    conn.commit()

def add_stock_code(conn, code, name, price):
    conn.execute(
        """
        INSERT OR REPLACE INTO Stock (
            code, name, price
        ) VALUES (
            ?, ?, ?
        );
        """,
        (code, name, price)
    )
    conn.commit()

def add_stock_quantity(conn, code, quantity):
    conn.execute(
        """
        UPDATE Stock
        SET quantity = quantity + ?
        WHERE code = ?
        """,
        (quantity, code)
    )
    conn.commit()

def buy_stock(conn, code, quantity):
    result = conn.execute("SELECT quantity, price FROM Stock WHERE code = ?", (code,)).fetchone()
    if not result:
        raise ValueError('No entry for code {}'.format(code))
    on_hand, price = result
    if on_hand < quantity:
        raise ValueError('Cannot buy {}, only {} on hand'.format(quantity, on_hand))
    conn.execute(
        """
        UPDATE Stock
        SET quantity = quantity - ?
        WHERE code = ?
        """,
        (quantity, code)
    )
    conn.commit()
    return quantity * price

def main():
    conn = sqlite3.connect(DATABASE)

    # create some test data
    make_stock_table(conn)
    add_stock_code(conn, 2429, "Golden Delicious Apples", 249)
    add_stock_quantity(conn, 2429, 20)
    add_stock_code(conn, 2514, "Macintosh Apples", 179)
    add_stock_quantity(conn, 2514, 35)

    # sell
    while True:
        code = get_int("Enter product GTIN-8 code (or 0 to quit): ")
        if code == 0:
            break
        quantity = get_int("How many would you like? ")
        try:
            cost = buy_stock(conn, code, quantity)
            print("Cost is {}".format(money_str(cost)))
        except ValueError as ve:
            print(ve)

if __name__ == "__main__":
    main()

尝试使用python检查代码是否保存在文本文件中

3 个答案: