你如何在python中找到带引号的数字列表的平均值？

I have two types of lists. The first without quotes, which works and prints the average fine:

我有两种类型的列表。第一个没有引号，工作和打印平均罚款：

l = [15,18,20]
print l
print "Average: ", sum(l)/len(l)

This prints:

这打印：

[15,18,20]
Average: 17

The second list has numbers with quotes, which returns an error:

第二个列表的数字带引号，返回错误：

x = ["15","18","20"]
print x
print "Average: ", sum(x)/len(x)

The Error is:

错误是：

TypeError: unsupported operand type(s) for +: 'int' and 'str'

How do you calculate a list with number values within quotes?

如何计算数字值在引号内的列表？

3 个解决方案

#1

The quotes mean that you have a list of strings:

引号表示您有一个字符串列表：

>>> x = ["15","18","20"]
>>> type(x[0])
<type 'str'>
>>>

sum only works with lists of numbers (integers such as 1 or floats such as 1.0).

sum仅适用于数字列表（整数，如1或浮点数，如1.0）。

To fix your problem, you must first convert your list of strings into a list of integers. You can use the built-in map function for this:

要解决您的问题，您必须先将您的字符串列表转换为整数列表。您可以使用内置的map函数：

x = ["15","18","20"]
x = map(int, x)

Or, you could use a list comprehension (which many Python programmers prefer):

或者，您可以使用列表理解（许多Python程序员更喜欢）：

x = ["15","18","20"]
x = [int(i) for i in x]

Below is a demonstration:

以下是演示：

>>> x = ["15","18","20"]
>>> x = map(int, x)
>>> x
[15, 18, 20]
>>> type(x[0])
<type 'int'>
>>> sum(x) / len(x)
17
>>>

#2

you need to convert them to int first:

你需要先将它们转换为int：

x = ["15","18","20"]
print sum(map(int,x))/len(x)

here map will map every element of x to integer type

这里map将x的每个元素映射到整数类型

#3

print "Average of {list} is: {avg}".format(
    list=l,
    avg=sum(int(x) for x in l) / len(l),
)

#1