How to initialize a ctypes array in Python from command line

Question

So I have been tasked with writing a Python script which accesses a Win 32 DLL to perform some functionality. This script needs to accept parameters from the command line then output other parameters.

I am using ctypes since it is the easiest way I have found to pass parameters to the Win 32 DLL methods but I was lucky enough to have a fixed array of values from the command line which I solved by doing such:

seed = (ctypes.c_ubyte * 12)(
    ctypes.c_ubyte(int(sys.argv[3], 16)), ctypes.c_ubyte(int(sys.argv[4], 16)),
    ctypes.c_ubyte(int(sys.argv[5], 16)), ctypes.c_ubyte(int(sys.argv[6], 16)),
    ctypes.c_ubyte(int(sys.argv[7], 16)), ctypes.c_ubyte(int(sys.argv[8], 16)),
    ctypes.c_ubyte(int(sys.argv[9], 16)), ctypes.c_ubyte(int(sys.argv[10], 16)),
    ctypes.c_ubyte(int(sys.argv[11], 16)), ctypes.c_ubyte(int(sys.argv[12], 16)),
    ctypes.c_ubyte(int(sys.argv[13], 16)), ctypes.c_ubyte(int(sys.argv[14], 16))
)

But this is not dynamic in anyway and I tried to perform this array initialization with a for loop inside the array initialization but without success.

I am completely new to Python and find it rather difficult to do what I consider simple tasks in other languages (not bashing the language, just not finding it as intuitive as other languages for such tasks).

So, is there a way to simplify initializing this array where there could be a variable amount of entries per se?

I have searched and searched and nothing I have found has solved my problem.

All positive and negative comments are always appreciated and both will always serve as a learning experience :)

Mark Tolonen · Accepted Answer · 2018-11-21 08:53:12Z

5

From your example it looks like you have 14 parameters and the last 12 are hexadecimal bytes.

import ctypes
import sys

# Convert parameters 3-14 from hexadecimal strings to integers using a list comprehension.
L = [int(i,16) for i in sys.argv[3:15]]

# Initialize a byte array with those 12 parameters.
# *L passes each element of L as a separate parameter.
seed = (ctypes.c_ubyte * 12)(*L)

answered Nov 21, 2018 at 8:53

Mark Tolonen

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1 Comment

CCS Over a year ago

Thank you for your solution, I chose it as the answer because it is more anonymous method like, and only took two lines of code :) Thanks again for taking the time to answer, much appreciate!

Hao Li · Accepted Answer · 2018-11-21 05:31:22Z

3

Try this:

seed_list = []                   
for i in sys.argv[3:]:
    seed_list.append(ctypes.c_ubyte(int(i, 16)))
seed = (ctypes.c_ubyte * len(seed_list))(*seed_list)

answered Nov 21, 2018 at 5:31

Hao Li

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2 Comments

CCS Over a year ago

I wish I could select both response as solutions because they both worked as expected. Thank you for your solution.

CCS Over a year ago

But this did allow me to initialize a large array which much less code, thanks again!

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