Encode Bytes

[albert_k_arhin]

Hi All,
I am new to python and I am using a strip down version of
python that does not support struc,pack,etc.

I have a binary protocol that is define as follows:

PART OffSet Lenght
=============== =============
ID 0 2
VER 2 1
CMD 3 2
PGKID 5 2
DATE 7 3
TIME 10 3
CRC 13 2
DLEN 15 2

How do I encode these the offset is in Bytes.

Thank you very much.

[John Machin]

Re: Encode Bytes

On Jul 12, 4:40 am, "albert_k_arhin " <albert_k_ar... @yahoo.comwrote :

Hi All,
I am new to python and I am using a strip down version of
python that does not support struc,pack,etc.
>
I have a binary protocol that is define as follows:
>
PART OffSet Lenght
=============== =============
ID 0 2
VER 2 1
CMD 3 2
PGKID 5 2
DATE 7 3
TIME 10 3
CRC 13 2
DLEN 15 2
>
How do I encode these the offset is in Bytes.
>

You haven't defined your data precisely enough to allow use of
struct.pack even if it were available to you.

Are all of the 1-byte fields unsigned integers (range 0 to 255
inclusive), or are some signed (range -128 to 127)?
Are all of the 2-byte fields unsigned integers (range 0 to 65535
inclusive) or are some signed (-32768 to 32767)?
What is the format of the 3-byte DATE and TIME fields? What type is
your starting value -- datetime.dateti me?
Littlendian or bigendian?

Here's an example of the sort of function you'll need to write:

>>def packu2le(anint) :

.... """Produce a 2-byte littlendian string from an unsigned
integer"""
.... assert 0 <= anint <= 65535
.... byte0 = anint & 0xff
.... byte1 = anint >8
.... return chr(byte0) + chr(byte1)
....

>>packu2le(0)

'\x00\x00'

>>packu2le(25 5)

'\xff\x00'

>>packu2le(25 6)

'\x00\x01'

>>packu2le(6553 5)

'\xff\xff'

>>packu2le(-1)

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 2, in packu2le
AssertionError

>>>

HTH,
John