Converting a list of integers to binary "string" in python

Question

I have a list of numbers that I would like to send to the socket connection as binary data.

As an example, I start with the following list:

data = [2,25,0,0,ALPHA,0,23,18,188] 

The above ALPHA list can have any value between 1 and 999. I originally converted this to a string using

  hexdata = ''.join([chr(item) for item in data]) 

So, if ALPHA is 101, this will return the following line:

 >>> data = [2,25,0,0,101,0,23,18,188] >>> hexdata = ''.join([chr(item) for item in data]) >>> hexdata '\x02\x19\x00\x00e\x00\x17\x12\xbc' 

This works fine, and '\ x02 \ x19 \ x00 \ x00e \ x00 \ x17 \ x12 \ xbc' is the line I need to send.

However, this does not work for ALPHA values ​​that exceed 255 because it is outside the range of the chr statement. If, for example, ALPHA were 999, I would like to get the following line:

 data = [2,25,0,0,999,0,23,18,188] hexdata = '\x02\x19\x00\x03\xed\x00\x17\x12\xbc' 

I looked at the documentation for struct.pack (), but I cannot figure out how this can be used to achieve the above line. ALPHA is the only variable in the list.

Any help would be greatly appreciated.

EDIT 1

What kind of behavior do you want? Anything between 256 and 65535 takes 2 bytes to represent. Do you want to unpack it the other side? Update the message with your intentions. - gahooa 1 min. Back

That's right, since 999 is above threshold 256, it is represented by two bytes:

 data = [2,25,0,0,999,0,23,18,188] hexdata = '\x02\x19\x00**\x03\xed**\x00\x17\x12\xbc' 

It makes sense?

As for unpacking, im only sends this data to the socket, I get the data, but this has already been taken care of.

EDIT 2

The string I am sending is always of a fixed length. For simplicity, I find it best to present the list as follows:

 ALPHA = 101 data = [25,alpha1,alpha2,1] hexdata = '\x19\x00e\x01' ALPHA = 301 data = [25,alpha1,alpha2,1] hexdata = 'x19\x01\x2d\x01' 

as you can see in the hexdata line, it will look like this: \ x01 \ x2d \

If ALPHA <256, alpha1 = 0.

Answer 1

Do you want to send one byte for ALPHA if it is <256, but two bytes if> = 256? It seems strange - how does the recipient find out what is the matter ... ???

But if this is what you want, then

 x = struct.pack(4*'B' + 'HB'[ALPHA<256] + 4*'B', *data) 

- one way to achieve this.

Answer 2

If you know the data and position of ALPHA in advance, it is best to use struct.pack with a large endpoint for this position and omit 0, which can be overwritten:

 def output(ALPHA): data = [2,25,0,ALPHA,0,23,18,188] format = ">BBBHBBBB" return struct.pack(format, *data) output(101) # result: '\x02\x19\x00\x00e\x00\x17\x12\xbc' output(999) # result: '\x02\x19\x00\x03\xe7\x00\x17\x12\xbc' 

Answer 3

You can use python array

 import array a = array.array('i') a.extend([2,25,0,0,101,0,23,18,188]) output = a.tostring() 

Answer 4

Bytes cannot have a value greater than 255, so with ALPHA exceeding 255, you need to somehow split it into two bytes. This can be done like this:

 high, low = divmod(ALPHA, 255) 

You can then insert high and low values ​​into the list of values.

There are other options, such as using bytearray (in version 2.6) or struct.pack, etc., but in the end you will have to somehow convert this number to two bytes.

Answer 5

Do you want to send one byte for ALPHA if it is <256, but two bytes if> = 256?

another (perhaps more general) way:

 x = reduce(lambda x, y: x + y, map(lambda x: struct.pack('B', x), data))