how to create a "byte stream" from different data type in python

Question

Here is a little problem: I want to create a byte stream (a table of byte integer) from different data type, integer of variable length, string.

val1 = 0x2
val2 = 0x0001020304050607
val3 = "blablabla"

And I want to obtain a stream like:

byteStream = val1 + val2 + val3
byteStream = [0x02, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x62, 0x6c, 0x61, 0x62, 0x6c, 0x61, 0x62, 0x6c, 0x61]

I have tried several things, like using a intermediate string and then convert this in byte. But this solution is ugly, and does not work properly.

Any help welcomed. Thanks.

unutbu · Accepted Answer · 2011-08-30 16:04:10Z

3

import struct

val1 = 0x2
val2 = 0x0001020304050607
val3 = "blablabla"

data=struct.pack('>BQ9s',val1,val2,val3)
print repr(data)

yields

'\x02\x00\x01\x02\x03\x04\x05\x06\x07blablabla'

BQ9s tells struct.pack to pack one unsigned int (1 byte) , followed by one unsigned long long (8 bytes) followed by 9 chars (1 byte each). The list of possible format characters can be found here.

data is a string (that is, a sequence of bytes). If you wish to ultimately have a list, you could use list(data).

edited Aug 30, 2011 at 16:04

answered Aug 30, 2011 at 15:55

unutbu

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2 Comments

Xavier Combelle Over a year ago

where are methods to_bytes and from_bytes I did not found on the dic

unutbu Over a year ago

@Xavier Combelle: to_bytes is new ... introduced in Python 3.2

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