SQLAlchemy | Technology Tales

Avoiding Python missing package errors with automatic installation checks

20^th October 2025

Though some may not like having something preceding package import statements in Python scripts, I prefer the added robustness of an extra piece of code checking for package presence and installing anything that is missing in place getting an error. In what follows, I define the list of packages that need to be present for everything to work:

required_packages = ["pandas", "tqdm", "progressbar2", "sqlalchemy", "pymysql"]

Then, I declare the inbuilt modules in advance of looping through the list that was already defined (adding special handling for a case where there has been a name change):

import subprocess
import sys
for package in required_packages:
    try:
        __import__(package if package != "progressbar2" else "progressbar")
        print(f"{package} is already installed.")
    except ImportError:
        print(f"{package} not found. Installing...")
        subprocess.check_call([sys.executable, "-m", "pip", "install", package])

The above code tries importing the package and catches the error to do the required installation. While a stable environment may be a better way around all of this, I find that this way of working adds valuable robustness to a script and automates what you would need to do anyway. Though the use of requirements files and even the Poetry tool for dependency management may be next steps, this approach suffices for my simpler needs, at least when it comes to personal projects.

Building a sitemap in XML

24^th November 2022

While there are many tools that will build XML site maps, there is some satisfaction to be had in creating your own. This is despite there being a multitude of search engine optimisation plugins for content management systems like WordPress or what is built into static site generators like Hugo. Sometimes, building your own allows for added simplicity, and that is shared with recent efforts in WordPress theme development.

The sitemap XML protocol is simple enough to offer a short coding project. The basis was what Hugo generates, and I used Python to create the XML files. The only libraries that I needed were configparser, SQLAlchemy and pandas. The first two of these allowed databases to be queried, and the last on the list was used for data processing. Otherwise, it was a case of using what is built into the Python language, like file writing and looping.

Once the scripts were ready, they could be uploaded to web servers and executed by scheduled jobs using CRON to keep things up to date. Along the way, I also uncovered a way to publicise the locations of the sitemap files to search engine bots using robots.txt. The structure of the instruction is the following:

User-agent: * Sitemap: sitemap.xml

This means that it announces to all bots the location of the sitemap file. In my case, I always included the full URL for the XML file, and that clearly varies by website location.