Java 如何在python中将字节数组转换为双精度数？
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How can I convert a byte array to a double in python?
提问by user2426316
I am using Java to convert a double into a byte array. Like this:
我正在使用 Java 将双精度转换为字节数组。像这样：
public static byte[] toByteArray(double value) {
byte[] bytes = new byte[8];
ByteBuffer.wrap(bytes).putDouble(value);
return bytes;
}
Now, I would like to convert this byte array back into a double. In Java I would do it like this:
现在，我想将此字节数组转换回双精度。在 Java 中，我会这样做：
public static double toDouble(byte[] bytes) {
return ByteBuffer.wrap(bytes).getDouble();
}
Now, how can I write the toDouble()method in Python?
现在，我如何toDouble()在 Python 中编写该方法？
采纳答案by Martijn Pieters
Python has the structmoduleto convert bytes back to floatvalues:
Python 具有将字节转换回值的struct模块float：
import struct
value = struct.unpack('d', bytes)[0]
Here 'd'signifies that a double value is expected (in native endianess, as 8 bytes). See the module documentation for more options, including specifying endianess.
这里'd'表示需要一个双精度值（在本机字节序中，为 8 个字节）。有关更多选项，包括指定字节顺序，请参阅模块文档。
Another option is to turn your bytesvalue into an arrayobject; you'd use this is if you had a homogenous sequence of doubles:
另一种选择是将您的bytes价值变成一个array对象；如果你有一个同构的双打序列，你会使用这个：
import array
doubles_sequence = array.array('d', bytes)
where every 8 bytes is interpreted as a double value, making doubles_sequencea sequence of doubles, addressable by index. To support a different endianess, you can swap the byte order with doubles_sequence.byteswap().
其中每 8 个字节被解释为一个双doubles_sequence精度值，形成一个双精度序列，可通过索引寻址。要支持不同的字节序，您可以将字节顺序与doubles_sequence.byteswap().
回答by abarnert
You want the structmodule:
你想要的struct模块：
>>> d = 1.234
>>> b = struct.pack('d', d)
>>> b
b'X9\xb4\xc8v\xbe\xf3?'
>>> d2, = struct.unpack('d', b)
>>> d2
1.234
The packmethod gives you a bytesin Python 3.x, or a strin Python 2.x. This type isn't mutable like a Java byte[], and in 2.x it also acts like a sequence of single-character strings, not a sequence of numbers from 0-255. If you need to fix either of those, just convert it to bytearray.
该pack方法bytes在 Python 3.x 中为您提供了一个，或者str在 Python 2.x 中为您提供了一个。这种类型不像 Java 那样可变byte[]，在 2.x 中它也像一个单字符串序列，而不是从 0 到 255 的数字序列。如果您需要修复其中任何一个，只需将其转换为bytearray.
Also, note that—in both Java and Python—you probably want to specify an explicit endianness more often than not, especially if you're planning to save the bytes to a file or send them over the network. See Format Stringsfor details.
另外，请注意，在 Java 和 Python 中，您可能希望经常指定显式字节序，尤其是在您计划将字节保存到文件或通过网络发送它们时。有关详细信息，请参阅格式字符串。
So:
所以：
>>> b = bytearray(struct.pack('!d', d))
>>> b
bytearray(b'?\xf3\xbev\xc8\xb49X')
>>> b[0]
63
