Map 对象在 Python 3 中没有 len()
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Map object has no len() in Python 3
提问by user3219624
I have this Python tool written by someone else to flash a certain microcontroller, but he has written this tool for Python 2.6 and I am using Python 3.3.
我有其他人编写的这个 Python 工具来刷新某个微控制器，但他为 Python 2.6 编写了这个工具，我使用的是 Python 3.3。
So, most of it I got ported, but this line is making problems:
所以，大部分我都被移植了，但这条线正在制造问题：
data = map(lambda c: ord(c), file(args[0], 'rb').read())
The filefunction does not exist in Python 3 and has to be replaced with open. But then, a function which gets dataas an argument causes an exception: “TypeError: object of type 'map' has no len()”.
该file函数在 Python 3 中不存在，必须替换为open. 但是，data作为参数获取的函数会导致异常：“TypeError: object of type 'map' has no len()”。
But what I see so far in the documentation is, that maphas to join iterable types to one big iterable, am I missing something?
但是到目前为止我在文档中看到的是，map必须将可迭代类型加入一个大的可迭代类型，我是否遗漏了什么？
What do I have to do to port this to Python 3?
我需要做什么才能将它移植到 Python 3？
采纳答案by thefourtheye
In Python 3, mapreturns an iterator. If your function expects a list, the iterator has to be explicitly converted, like this:
在 Python 3 中，map返回一个迭代器。如果您的函数需要一个列表，则必须显式转换迭代器，如下所示：
data = list(map(...))
And we can do it simply, like this
我们可以简单地做到这一点，就像这样
with open(args[0], "rb") as input_file:
data = list(input_file.read())
rbrefers to read in binary mode. So, it actually returns the bytes. So, we just have to convert them to a list.
rb指以二进制方式读取。所以，它实际上返回字节。因此，我们只需要将它们转换为列表。
Quoting from the open's docs,
引自open's docs,
Python distinguishes between binary and text I/O. Files opened in binary mode (including 'b' in the mode argument) return contents as bytes objects without any decoding.
Python 区分二进制和文本 I/O。以二进制模式打开的文件（包括 mode 参数中的“b”）将内容作为字节对象返回，无需任何解码。
