[英]Pack and Unpack Bits and Bytes in Python
I am new to Python (I'm using Python3) and programming in general. 我是Python(我正在使用Python3)和编程的新手。 Could you please provide a detailed explanation on how pack and unpack produce an answer in python;
您能否详细说明如何打包和解包在python中产生答案; I know the syntax for using both functions but I do not understand how the answer is calculated.
我知道使用这两种功能的语法,但是我不明白答案的计算方式。 For example, I do not understand why the following code:
例如,我不明白为什么下面的代码:
L = struct.pack('f', 255) print([ii for ii in L])
would produce the following output (especially why there is 127 and 67): 会产生以下输出(尤其是为什么有127和67):
[0, 0, 127, 67]
Also, why the following code: 另外,为什么下面的代码:
LL = struct.unpack('i', b'0000') print(LL)
would produce the following number: 将产生以下数字:
(808464432,)
Thanks for the help. 谢谢您的帮助。
In the first case you're seeing the decimal values of the 4 bytes that make up a 32bit floating point number . 在第一种情况下,您将看到组成一个32位浮点数的4个字节的十进制值。
In your specific example, the floating point number 255.0 is represented in memory as 4 bytes with hexadecimal values of 43 7f 00 00
. 在您的特定示例中,浮点数255.0在内存中表示为4个字节,十六进制值为
43 7f 00 00
。 Since you're on a little-endian platform, you see the least significant byte first. 由于您使用的是低端字节序平台,因此首先会看到最低有效字节。 Hence, converted into a list of bytes, you have
因此,将其转换为字节列表
[ 0x00, 0x00, 0x7f, 0x43 ]
Converted to decimal values you obtain 转换为您获得的十进制值
[0, 0, 127, 67]
In the second case, you try to interpret the result of b'0000'
. 在第二种情况下,您尝试解释
b'0000'
的结果。
>>> type(b'0000')
<class 'bytes'>
>>> len(b'0000')
4
As you can see, this expression returns a sequence of 4 bytes, so in this case it will be a sequence of 4 instances of the character 0
. 如您所见,该表达式返回4个字节的序列,因此在这种情况下它将是字符
0
的4个实例的序列。
>>> '%x' % ord('0')
'30'
The value of the character 0
is 0x30
in hexadecimal. 字符
0
的值是十六进制的0x30
。 The 4 bytes interpreted as a 32bit integer are equivalent to the hexadecimal value of 0x30303030
. 解释为32位整数的4个字节等效于十六进制值
0x30303030
。
>>> 0x30303030
808464432
When we write this value in decimal, we obtain 808464432
. 当我们用十进制写这个值时,我们得到
808464432
。
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