How to struct.pack() a variable length list in Python

Question

For example when len(args) = 2:

args = []
args.append('arg1')
args.append('argument2')

bytes = struct.pack('B' * len(args), len(args[0]), len(args[1]))

However, I need to handle variable-length args, that is, len(args) = n, where n is any positive integer.

I think the module was designed for a C-like definition of struct, which never changes size. — Mark Ransom
– Mark Ransom, Commented Apr 14, 2014 at 1:17

emesday · Accepted Answer · 2014-04-14 01:47:26Z

3

Try:

bytes = struct.pack('B' * len(args), *[len(x) for x in args])

To unpack this:

struct.unpack('B' * len(bytes), bytes)

Because 'B' means 1-byte unsigned char, len(bytes) can be length of it.

edited Apr 14, 2014 at 1:47

answered Apr 14, 2014 at 1:13

emesday

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1 Comment

Florian Mayer Over a year ago

The problem is more about how to unpack this again.

dstromberg · Accepted Answer · 2014-04-14 02:36:27Z

0

You probably should add a length field to your output, so you know how many things to read back in. Or rather use a "number of strings" followed by "length of string1", "length of string2", ..., "length of stringn".

answered Apr 14, 2014 at 2:36

dstromberg

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