Category Archives: Python

Self hosting and installing from pip repos

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I have an application that I want to share with my team. Fortunately, we have a shared server, so it is pretty easy to do so: if I put a file in /usr/local/bin it can A) be executed by anyone on the server and B) will not interfere with RPM packages. But, I do potentially want to put this code on other machines as well, so I am going to buld it as a pip package, upload it to a team repo (apache HTTPD instance on this machine) and then install it from pip as root.

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Converting a Shell Script to Python

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We have a build system that has grown organically. It started as a shell script. We needed to run it from gitlab, so we wrote helper scripts to insulate our code from gitlab. Then we added some helper functions to mimic the gitlab interactions when working with them from the comand line. The helper functions grew until you could not practically run the original shell script without them.

It is a mess.

I want to refactor it.

Refactoring Shell is painful.

I want objects. I want python.

So I am rewriting the gitlab and functions layer in python with an eye to rewriting the whole thing. Here’s what I have learned;

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Long Refactoring: Generators

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While the main solving function is now cleaned up, I am not very happy with the code that checks the validation on each cell.

I am not going to go through each step here, as the pattern is well established now. Pull out of the function anything that is a distractor. Once you have the heart of the algorithm, clean it up. Then put things back together.

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Long Refactoring: Backtracking

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Now that I have cleaned the loop up somewhat, we can continue with the process of refactoring the code. This is a continuation to the article series I started here.

This next step really moves beyond refactoring. I have identified that the intended backtracking was not actually implemented in the code. Instead, The whole board is wiped and restarted many times, causing a decent slowdown in execution. My refactoring process thus far has allowed me to understand the code well enough to attempt and improvement.

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Long Refactoring: More loop cleanup

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In my last article on the Long Refactoring series, I elided the process I went through to solve the bug. While preparing to turn the articles into a presentation, I went through the steps myself again, and came across the bug. When I was writing the articles, I was pressed for time, and didn’t go through the process of solving it step by step, which in turn means there is a gap between the pre-and-post states of the code: you can’t get there from here.
Let me take it from where I mentioned that I found a bug, and added the unit test that shows it.

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socket system call from python

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While the Python socket API is mature, it does not yet support MCTP. I thought I would thus try to make a call from python into native code. The first step is to create a socket. Here is my code to do that.

Note that this is not the entire C code needed to make network call, just the very first step.I did include the code to read errno if the call fails.

#!/usr/bin/python3
from ctypes import *
libc = CDLL("/lib64/libc.so.6")
AF_MCTP = 45
SOCK_DGRAM  = 2
rc = libc.socket (AF_MCTP, SOCK_DGRAM, 0)
#print("rc = %d " % rc)
get_errno_loc = libc.__errno_location
get_errno_loc.restype = POINTER(c_int)
errno = get_errno_loc()[0]
print("rc = %d errno =  %d" % (rc, errno)   )
print("OK")

Running this code on my machine shows success

# ./spdm.py 
rc = 3 errno =  0
OK