Question

I need to use an embedded system running Python 1.5.2+ (!!!) with very few modules.
And there is no “struct” module usable…
Here is the list of usable modules :

marshal
imp
_main_
_builtin_
sys
md5
binascii

Yes that’s it, no struct module…

So, I need to create a 4 bytes representation of an unsigned short integer to send to serial…

With struct :

date = day + month * 32 + (year - 2000) * 512
time = 100 * hour + minute
data = struct.pack(b'HH', date, time)

date on 2 bytes time on 2 bytes and everybody’s happy…

But without using ‘struct’ module, how can I do that?

Answer 1

Here is a complete translation for you

Before

>>> import struct
>>> day = 1; month = 2; year = 2003
>>> hour = 4; minute = 5
>>> date = day + month * 32 + (year - 2000) * 512
>>> time = 100 * hour + minute
>>> data = struct.pack(b'HH', date, time)
>>> data
'A\x06\x95\x01'
>>> data.encode("hex")
'41069501'

And after

>>> data2 = chr(date & 0xFF) + chr((date >> 8) & 0xFF) + chr(time & 0xFF) + chr((time >> 8) & 0xFF)
>>> data2
'A\x06\x95\x01'
>>> data2.encode("hex")
'41069501'
>>>