Python：在舍入数字后使用 sum/len 求平均值

Question

我正在尝试构建一个程序，用户在该程序中以磅为单位输入地球上的重量（进入 ARRAY）。该程序将重量转换为它在月球上的重量。 然后最后，我希望它获取存储的数组并计算输入重量在月球上的平均重量。

使用下面的代码，它给了我“TypeError: 'float' object is not iterable”。 如何计算平均值？任何帮助表示赞赏！ 我的代码在这里link

numlist = list()
lbs = float(input("Enter a weight of person (Enter –1 to exit): "))
while (lbs != -1 ):
    numlist.append(lbs)
    moon_weight = (lbs / 9.81) * 1.622
    limited_float = round(moon_weight)
    print ('This person weighs', limited_float, 'pounds on the moon.')
    lbs = eval(input("Enter a next weight (Enter –1 to exit): "))

average = sum(moon_weight) / len(numlist)
print ('Average of weights on the moon:', average)

编辑： 因为while True 对我来说还是新的，我不想仅仅使用别人的工作。在其他人的大力帮助下，这就是我能够做到的。

numlist = list()
lbs = float(input("Enter a weight of person (Enter –1 to exit): "))
while (lbs != -1 ):
    moon_weight = (lbs / 9.81) * 1.622
    limited_float = round(moon_weight)
    numlist.append(moon_weight)
    print ('This person weighs', limited_float, 'pounds on the moon.')
    lbs = eval(input("Enter a next weight (Enter –1 to exit): "))

average = round(sum(numlist) / len(numlist))
print ('Average of weights on the moon:', average)

Answer 1

您需要将moon_weight 添加到numlist（而不是lbs），然后计算sum(numlist) / len(numlist) 而不是sum(moon_weight) / len(numlist)。

Answer 2

如果我理解正确，这就是你要找的。 我认为您将变量 moon_weight 与列表 numlist 混淆了。 下面是一个工作示例，说明如何做到这一点。

moon_weights_list = list()
while True:
    lbs = float(input("Enter a weight of person (Enter –1 to exit): "))
    if lbs == -1 :
        break

    moon_weight = (lbs / 9.81) * 1.622
    moon_weights_list.append(moon_weight)

    limited_float = round(moon_weight)
    print ('This person weighs', limited_float, 'pounds on the moon.')

average = sum(moon_weights_list) / len(moon_weights_list)
print('Average of weights on the moon:', average)

为了指出您遇到的具体问题，我将尝试解释这一行中出现的错误：

average = sum(moon_weight) / len(numlist)

错误：

TypeError: 'float' object is not iterable

由函数 sum() 引发，该函数将可迭代对象作为参数。

• 那么什么是可迭代对象？

1. 它是实现__iter__ 和__next__ 的类的实例。
2. 一个更简单的定义是：例如 for 循环可以迭代的东西。比如列表、集合、字典、类型等等......

回到你的代码，sum(moon_weight) 函数将moon_weight 作为参数，它应该包含一个浮点数，(moon_weight = (lbs / 9.81) * 1.622)。

代码如下：

average = sum(numlist) / len(numlist)

例如计算输入值的平均值（对于地球而不是月球）。

接下来是找到一种方法来创建一个包含月球值的列表，然后将其传递给两个函数 sum() 和 len()。正如我在上面包含的代码中所做的那样。

Answer 3

更正代码

numlist = [] # more standard than numlist = list()
while True:
    # Only need one input
    lbs = input("Enter a weight of person (Enter -1 to exit): ")
    if lbs == '-1' or lbs == '':
        break                           # done on -1 or empty string
    
    lbs = float(lbs)                    # float conversion
    moon_weight = (lbs/9.81)*1.622
    numlist.append(moon_weight)         # add moon weight
    print(f'This person weighs {round(moon_weight)} pounds on the moon')  # using string interpolation  # using string interpolation

# String interpolation and show two decimal places i.e. .2f
print(f'Average of weights on the moon: {sum(numlist) /len(numlist):.2f}')

测试

Enter a weight of person (Enter -1 to exit): 100
This person weighs 17 pounds on the moon
Enter a weight of person (Enter -1 to exit): 150
This person weighs 25 pounds on the moon
Enter a weight of person (Enter -1 to exit): 200
This person weighs 33 pounds on the moon
Enter a weight of person (Enter -1 to exit): -1
Average of weights on the moon: 24.80

说明

行：

print(f'Average of weights on the moon: {sum(numlist) /len(numlist):.2f}')

相当于：

average = sum(numlist) /len(numlist)
average_fmt = round(average, 2)        # round to 2 decimal places
print('Average of weights on the moon: ', average_fmt)

那是因为：

f'Average of weights on the moon: {sum(numlist) /len(numlist):.2f}' 

是一个字符串插值（即允许内部表达式被评估为最终字符串的特殊字符串）。

String interpolation的信息

带有 {} 的项目被评估为表达式。 {} 中的“:”标识允许添加格式说明符（例如“.2f”提供两位小数）。

更简单的 While 循环和输出

numlist = [] # more standard than numlist = list()
lbs = ''     # initial value so we will enter while loop
while lbs != -1:
    lbs = input("Enter a weight of person (Enter -1 to exit): ")
    if lbs != '-1':
      print(lbs)
      lbs = float(lbs)                    # float conversion
      moon_weight = (lbs/9.81)*1.622
      numlist.append(moon_weight)         # add moon weight
      print('This person weighs', round(moon_weight), 'pounds on the moon')  # using string interpolation  # using string interpolation
    else:
        break
     
if len(numlist) > 0:
    print('Average of weights on the moon: ', round(sum(numlist) /len(numlist), 2))
else:
    print('No weights entered')