Jupyter iPython Notebook和命令行产生不同的结果(Jupyter iPython Notebook and Command Line yield different result

Jupyter iPython Notebook和命令行产生不同的结果(Jupyter iPython Notebook and Command Line yield different results)

我有以下Python 2.7代码：

def average_rows2(mat): ''' INPUT: 2 dimensional list of integers (matrix) OUTPUT: list of floats Use map to take the average of each row in the matrix and return it as a list. Example: >>> average_rows2([[4, 5, 2, 8], [3, 9, 6, 7]]) [4.75, 6.25] ''' return map(lambda x: sum(x)/float(len(x)), mat)

当我使用iPython笔记本在浏览器中运行它时，我得到以下输出：

[4.75, 6.25]

但是，当我在命令行（Windows）上运行代码的文件时，出现以下错误：

>python -m doctest Delete.py ********************************************************************** File "C:\Delete.py", line 10, in Delete.average_rows2 Failed example: average_rows2([[4, 5, 2, 8], [3, 9, 6, 7]]) Expected: [4.75, 6.25] Got: <map object at 0x00000228FE78A898> **********************************************************************

为什么命令行抛出一个错误？ 有没有更好的方式来构建我的功能？

I have the following Python 2.7 code:

def average_rows2(mat): ''' INPUT: 2 dimensional list of integers (matrix) OUTPUT: list of floats Use map to take the average of each row in the matrix and return it as a list. Example: >>> average_rows2([[4, 5, 2, 8], [3, 9, 6, 7]]) [4.75, 6.25] ''' return map(lambda x: sum(x)/float(len(x)), mat)

When I run it in my browser using iPython notebook, I get the following output:

[4.75, 6.25]

However, when I run the code's file on Command Line (Windows), I get the following error:

>python -m doctest Delete.py ********************************************************************** File "C:\Delete.py", line 10, in Delete.average_rows2 Failed example: average_rows2([[4, 5, 2, 8], [3, 9, 6, 7]]) Expected: [4.75, 6.25] Got: <map object at 0x00000228FE78A898> **********************************************************************

Why does the command line toss an error? Is there a better way to structure my function?

最满意答案

看起来您的命令行正在运行Python 3.内置map返回Python 2中的列表，但在Python 3中返回一个迭代器（一个map对象）。要将后者转换为列表，请将list构造函数应用于它：

# Python 2 average_rows2([[4, 5, 2, 8], [3, 9, 6, 7]]) == [4.75, 6.25] # => True # Python 3 list(average_rows2([[4, 5, 2, 8], [3, 9, 6, 7]])) == [4.75, 6.25] # => True

It seems like your command line is running Python 3. The builtin map returns a list in Python 2, but an iterator (a map object) in Python 3. To turn the latter into a list, apply the list constructor to it:

# Python 2 average_rows2([[4, 5, 2, 8], [3, 9, 6, 7]]) == [4.75, 6.25] # => True # Python 3 list(average_rows2([[4, 5, 2, 8], [3, 9, 6, 7]])) == [4.75, 6.25] # => True