为什么python2和python3的print输出同一个字符串不同?

问题描述

在python2中:

$ python2 -c 'print "x08x04x87x18"' | hexdump -C
00000000  08 04 87 18 0a                                    |.....|
00000005

在python3中:

$ python3 -c 'print("x08x04x87x18")' | hexdump -C
00000000  08 04 c2 87 18 0a                                 |......|
00000006

为什么这里有字节"xc2"?

编辑:

我认为当字符串具有非 ascii 字符时，python3 会将字节 "xc2" 附加到字符串.(正如@Ashraful Islam 所说)

I think when the string have a non-ascii character, python3 will append the byte "xc2" to the string. (as @Ashraful Islam said)

那么如何在 python3 中避免这种情况?

So how can I avoid this in python3?

推荐答案

考虑以下代码片段:

import sys
for i in range(128, 256):
    sys.stdout.write(chr(i))

使用 Python 2 运行它并使用 hexdump -C 查看结果:

Run this with Python 2 and look at the result with hexdump -C:

00000000  80 81 82 83 84 85 86 87  88 89 8a 8b 8c 8d 8e 8f  |................|

等等.没有惊喜；从 0x80 到 0xff 的 128 个字节.

Et cetera. No surprises; 128 bytes from 0x80 to 0xff.

对 Python 3 执行相同操作:

Do the same with Python 3:

00000000  c2 80 c2 81 c2 82 c2 83  c2 84 c2 85 c2 86 c2 87  |................|
...
00000070  c2 b8 c2 b9 c2 ba c2 bb  c2 bc c2 bd c2 be c2 bf  |................|
00000080  c3 80 c3 81 c3 82 c3 83  c3 84 c3 85 c3 86 c3 87  |................|
...
000000f0  c3 b8 c3 b9 c3 ba c3 bb  c3 bc c3 bd c3 be c3 bf  |................|

总结:

• 从 0x80 到 0xbf 的所有内容都添加了 0xc2.
• 从 0xc0 到 0xff 的所有内容都将第 6 位设置为零，并在前面添加了 0xc3.

• Everything from 0x80 to 0xbf has 0xc2 prepended.
• Everything from 0xc0 to 0xff has bit 6 set to zero and has 0xc3 prepended.

那么，这里发生了什么?

So, what’s going on here?

在 Python 2 中，字符串是 ASCII 并且不进行转换.告诉它写一些超出 0-127 ASCII 范围的内容，它会说oky-doke！"和只写那些字节.简单.

In Python 2, strings are ASCII and no conversion is done. Tell it towrite something outside the 0-127 ASCII range, it says "okey-doke!" andjust writes those bytes. Simple.

在 Python 3 中，字符串是 Unicode.当非 ASCII 字符写，它们必须以某种方式编码.默认编码是UTF-8.

In Python 3, strings are Unicode. When non-ASCII characters arewritten, they must be encoded in some way. The default encoding isUTF-8.

那么，这些值是如何以 UTF-8 编码的?

So, how are these values encoded in UTF-8?

从 0x80 到 0x7ff 的代码点编码如下:

Code points from 0x80 to 0x7ff are encoded as follows:

110vvvvv 10vvvvvv

其中 11 个 v 字符是代码点的位.

Where the 11 v characters are the bits of the code point.

因此:

0x80                 hex
1000 0000            8-bit binary
000 1000 0000        11-bit binary
00010 000000         divide into vvvvv vvvvvv
11000010 10000000    resulting UTF-8 octets in binary
0xc2 0x80            resulting UTF-8 octets in hex

0xc0                 hex
1100 0000            8-bit binary
000 1100 0000        11-bit binary
00011 000000         divide into vvvvv vvvvvv
11000011 10000000    resulting UTF-8 octets in binary
0xc3 0x80            resulting UTF-8 octets in hex

这就是为什么你在 87 之前得到一个 c2.

So that’s why you’re getting a c2 before 87.

如何在 Python 3 中避免这一切?使用 bytes 类型.

How to avoid all this in Python 3? Use the bytes type.

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