我的代码告诉我我需要浮动但是当我使用浮动时它告诉我“无法将'float'对象隐式转换为str”

Question

我不知道我做错了什么，请帮助:(
输出预期：

预期：

1. 项目名称：
2. 购买数量：
3. 单件价格：
4. 您要输入其他项目吗？输入“c”表示继续，输入“q”表示退出：
5. 1 牛奶 @ 2.99 美元 2.99 美元
6. 总计：2.99 美元

这是我的代码：

The task is broken down into three sections.
Section 1 - User Input
Section 2 - loop through the grocery list
Section 3 - provide output to the console

#Task: Create the empty data structure
grocery_item = {}
grocery_history = []

#Variable used to check if the while loop condition is met
stop = 'c'

while stop == 'c':

#Accept input of the name of the grocery item purchased.
  item_name = input("Item name:\n")

#Accept input of the quantity of the grocery item purchased.
  quantity = input("Quantity purchased:\n")   

#Accept input of the cost of the grocery item input (this is a per-item cost).
  cost = input("Price per item:\n")

    #Using the update function to create a dictionary entry which contains the name, number and price entered by the user.
  grocery_item['name'] = item_name        
  grocery_item['number'] = quantity 
  grocery_item['price'] = float(cost)
  grocery_item = {'name':item_name,'number':quantity,'price':cost}
    #Add the grocery_item to the grocery_history list using the append function
  grocery_history.append(grocery_item)

    #Accept input from the user asking if they have finished entering grocery items.
  stop = input("Would you like to enter another item?\n Type 'c' for continue or 'q' to quit:\n")

# Define variable to hold grand total called 'grand_total'
  grand_total = 0
#Define a 'for' loop.  

for items in range(0, len(grocery_history)):

  #Calculate the total cost for the grocery_item.
    item_total = int(grocery_history[items].get('number')) * float(grocery_history[items].get('price'))
  #Add the item_total to the grand_total
    grand_total = grand_total + float(item_total)
  #Output the information for the grocery item to match this example:
  #2 apple  @   $1.49   ea  $2.98

    print(grocery_history[items]['number'] + ' ' + str(grocery_history[items]['name']) + ' @ $' + str('%.2f' % grocery_history[items]['price']) + ' ea $' + str('%.2f' % item_total))


  #Set the item_total equal to 0
item_total = 0
#Print the grand total

print(str('Grand total: $%.2f' % grand_total))

'''

Answer 1

问题出在这四行：

grocery_item['name'] = item_name        
grocery_item['number'] = quantity 
grocery_item['price'] = float(cost)
grocery_item = {'name':item_name,'number':quantity,'price':cost}

最后一行结束了前三行，并将grocery_item['price'] 分配为 string 值，而不是 float。这会导致尝试将该值打印为带有%.2f 的浮点数的最终错误。

为什么第四行还在那里？只需将其删除。

Answer 2

轻松解决，只需将grocery_history 与str 包装起来

print(str(grocery_history[items]['number']) + ' ' + str(grocery_history[items]['name']) + ' @ $' + str('%.2f' % grocery_history[items]['price']) + ' ea $' + str('%.2f' % item_total)) 

此外，当您尝试将 float/int 添加到字符串时，会引发该错误，因为 python 希望您首先显式使用 @ 将 float/int 转换为字符串987654324@函数。

更新

使用 f-strings 打印更简洁：

print(f"{grocery_history[items]['number']} {grocery_history[items]['name']}  @ $ {grocery_history[items]['price']}  ea ${item_total}") 

现在你甚至不需要在你的花车上使用str。这仅适用于 python >= 3.6