Rubyist’s intro to Python web development

I have been using Ruby professionally for more than a decade now. Until recently, I haven’t explored much outside of the Ruby and Rails community. That changed however after I completed a course in Foundations of Data Science. This made me curious about Python and how to build applications using it.

Python and Ruby have many similarities. Both are interpreted, high-level programming languages. Python also has support for Object-Oriented Programming and Functional Programming. In terms of syntax, they have a similar look and feel, aside from some fundamental differences such as Python being indent-driven.

You may find this article to be very similar to the Ruby on Rails guide I posted years ago. This is not accidental since my goal is to introduce Python web application development to someone who is already familiar in the Ruby space.

Installing Python

The very first step is to install Python itself in your computer. I recommend using pyenv to manage your Python versions. pyenv is a Python version manager, like rbenv. In fact, pyenv is a fork of rbenv and is re-purposed for Python. To install pyenv:

curl | bash

After installing, update your login shell configuration by adding the following, e.g. in ~/.zshrc

export PATH="/home/user/.pyenv/bin:$PATH" eval "$(pyenv init -)" eval "$(pyenv virtualenv-init -)"

Now we are ready to use pyenv to install a specific Python version. But first, we need to install some dependencies so we can compile Python from source:

sudo apt-get install -y make build-essential libssl-dev zlib1g-dev libbz2-dev \
libreadline-dev libsqlite3-dev wget curl llvm libncurses5-dev libncursesw5-dev \
xz-utils tk-dev libffi-dev liblzma-dev python-openssl

Then, we can easily install a Python version, like 3.6.8 in this example:

pyenv install 3.6.8

If you are having trouble installing Python, it could be related to the OpenSSL version installed in your machine.

On Debian stretch (and Ubuntu bionic), libssl-dev is OpenSSL 1.1.x,
but support for that was only added in Python 2.7.13, 3.5.3 and 3.6.0.
To install earlier versions, you need to replace libssl-dev with
libssl1.0-dev. This is being tracked in

Once Python has been installed, you can opt to set the version (e.g 3.6.8) as your global version. This makes the Python executable available to all terminal sessions:

pyenv global 3.6.8

Package Management

pip is Python’s package manager, like rubygems or npm. If you installed Python, pip should also be available for you. If for some reason it is not installed, you can install it using the guide here.

curl -o $ python

Application-specific Packages

In Ruby/Rails we use the awesome library Bundler to handle application package management. We manage the packages using a Gemfile, and it gets converted into Gemfile.lock.

pipenv is similar to bundler, but its functionality extends beyond package management in the application. In this article we will use it similar to bundler so it will handle all the application package dependencies. To install pipenv, just use pip!

pip install pipenv

To specify the application packages, pipenv uses a Pipfile. An example is given below:

name = "pypi"
url = ""
verify_ssl = true


requests = "*"
flask = "*"
python-dotenv = "*"
flask-sqlalchemy = "*"
flask-migrate = "*"

python_version = "3.6" read more

Rubocop + vim

Rubocop + vim

Code linters such as Rubocop ensure consistent, clean code throughout your application. If all developers are using the same linter configuration, then you can be sure that any code that you encounter is organized in the same way regardless of the author.

One challenge in using linters is that it should have immediate feedback, or else it may disrupt the coding flow of the user. For example, you can run the linter manually after you make your changes, but as this is a manual process it can be easily forgotten.

Commit Hooks

To solve this, we can use pre-commit hooks (such as in git) to automatically run the linter script whenever we try to commit our changes. In this manner, it is an automated process and so will not be skipped in development.

For example, here is a git pre-commit hook for Rubocop (from and )

#!/usr/bin/env ruby
# put this file into your path and use `<file> install` to add a new hook
# or use it as a binary to check changed files

require 'shellwords'

if ARGV == ["install"]
exec "ln", "-sf", __FILE__, ".git/hooks/pre-commit"
raise unless ARGV == []

changed = `git status --porcelain`.
map { |l| l.split(" ", 2) }.
select { |status, _| ["A", "AM", "M"].include?(status) }.
map { |_, file| file.delete('"') }

exit if changed.empty?

result = `bundle exec rubocop --force-exclusion #{changed.shelljoin}`
puts result unless $?.success?
exit $?.exitstatus read more

DelayedJob Survival Guide

DelayedJob Survival Guide

One day at work I noticed that emails were taking much longer to be sent out from our app. I narrowed down the problem to our background queue which is responsible for sending out the emails. The solution prompted me to write this DelayedJob “survival guide”to help others who may encounter this issue in the future.

Asynchronous processing/background processing is an important part of a web application. This ensures that running code is not blocking the rest of the process if that code does not need to run synchronously. Common examples are sending emails or code that depends on a third-party API or service.

There are many solutions for this, such as Redis-backed programs like Sidekiq or Resque. There are also database-backed programs like DelayedJob. The advantage of using a database-backed solution is its simplicity: you don’t need an external dependency (such as Redis) to run it. Instead, you can use your existing database to manage your background processing.

This simplicity also has a disadvantage: you are now constrained by your database and database issues can directly affect your background processing.

The Problem

We had a new feature which required processing old data in the system. This uses the background queue as it takes a few seconds to process each individual task. Eventually these tasks accumulated, resulting in more than half a million jobs in the DelayedJob queue.

As I noticed that the queue is not getting processed as fast as I expected, I looked at the database logs. In the MySQL slow query logs, I noticed that almost all entries look like this:
UPDATE delayed_jobs
SET `delayed_jobs`.`locked_at` = '2018-06-05 11:48:28',
`delayed_jobs`.`locked_by` = 'delayed_job.2 host:ip-10-203-174-216 pid:3226'
WHERE ((run_at <= '2018-06-05 11:48:28'
AND (locked_at IS NULL OR locked_at < '2018-06-05 07:48:28') OR locked_by = 'delayed_job.2 host:ip-10-203-174-216 pid:3226')
AND failed_at IS NULL)
ORDER BY priority ASC, run_at ASC
DelayedJob updates the locking information (timestamp and PID) when processing jobs. However, this UPDATE call in the database does not use the index in the table, at least for old MySQL versions (5.6 or below). As the number of entries in the queue increases, this UPDATE call becomes much slower.

This is the problem with database-backed asynchronous queues: the database is used both as a state manager and the queue storage/retrieval, resulting in locking.

Emergency Processing

Since the queue processing is becoming really slow, some critical tasks were not being performed. Thus we needed to run some jobs manually (using the Ruby/Rails console). We can invoke a DelayedJob worker manually using this command:

However, we may want to run all tasks in a given queue, let’s say the important_queue. We can query the database for all tasks under the queue and invoke the worker manually for each:

Delayed::Job.where(queue: "important_queue").find_each do |dj|

In this manner we were able to quickly resolve some critical tasks that needed to be run immediately. However, this is not a scalable solution as everything is done manually. This also won’t solve the problem of having hundreds of thousands of tasks in the backlog.

Queue “Storage”

Searching the internet, I found that there were others who also encountered this problem. Their solution was documented here and here. The main gist of the solution is to temporarily remove most (or all) of the items in the delayed_jobs table into a separate table to “unclog” the background queue.

In this example, we will create a new table called delayed_jobs_storage with the same columns as the original delayed_jobs table. The examples also assume we are using MySQL as our database:

CREATE TABLE delayed_jobs_storage LIKE delayed_jobs;

Once the “storage” table has been created, we can now move the jobs into that new table. In this example, we will limit the query to only move jobs that are under the huge_queue queue.

INSERT INTO delayed_jobs_storage (SELECT * FROM delayed_jobs WHERE queue='huge_queue');

Then we remove the jobs that we moved from the original delayed_jobs table:

DELETE FROM delayed_jobs WHERE queue='huge_queue';

At this point, the background processing speed returns to normal as the size of the table is now greatly reduced. The next step is to gradually move back some jobs from the delayed_jobs_storage table into the delayed_jobs table so they are processed.

This involves some trial and error as we want to determine the optimal number of jobs that we can transfer. We want it so that we can move the largest amount of jobs without slowing down the queue. In my experiment, I determined that we can transfer up to around 100k jobs back to the queue without impacting the performance.

To move the first 100k jobs back into the delayed_jobs table:

INSERT INTO delayed_jobs (SELECT * FROM delayed_jobs_storage ORDER BY id ASC LIMIT 100000);

Then we need to remove those jobs from our “storage” table:

DELETE FROM delayed_jobs_storage ORDER BY id ASC LIMIT 100000;

We wait until all the jobs have been processed and the queue goes back to its minimal state. After which we repeat the process again until all of the jobs stored in delayed_jobs_storage have been moved back to the delayed_jobs table.


While this workaround will get you out of a bind when your backround queue is clogged, it is not a long-term solution. As much as possible we want to avoid this scenario happening in the first place!

Here are some ideas that you can implement:

  • Analyze each background job to see areas of optimization. If the code that is running in a job is not optimized, it will run slower and will consume more resources. Check your database queries and your code performance to make sure they are running as fast as possible. For example, add table indexes and remove N+1 queries.
  • Reorganize how you add jobs to the background queue. Sometimes we just add tasks to the queue without thinking about how it impacts the rest of the jobs. Can you make your code add less to the queue by removing redundancy? Does combining smaller jobs into a larger job make sense? Are longer-running jobs of lower priority than faster ones?
  • Consider moving to a Redis-based solution such as Sidekiq. This will make sure that your dependency to your main database is eliminated and allows you to use a separate (and more efficient) storage of your background jobs.

Photo by James Pond on Unsplash read more

Late-to-the-party guide to Vim and Tmux

Late-to-the-party guide to Vim and Tmux

In my first job we used Emacs as our main text editor. However, I have no idea how to use it properly so I just used it more like Notepad++ than Emacs. In our team there is one person who refused to use Emacs, instead he was using vi (without the m!). To be honest, it looked painful watching him edit code with no syntax highlighting, no line numbers, and no plugins whatsoever. We tried constantly to convince him to use Emacs but he always refused and stuck to using vi. I thought the guy was crazy.

Fast forward 12 years in my career. I was attending a Ruby conference with my peers and one of the speakers (Brad Urani) demonstrated zshell, vim, and tmux and how he does development in his machine. It looked cool! Some of my peers also uses vim and tmux so its not a new concept to me, however I always decided to use gedit all these years. This time, they probably thought I was crazy.

After the conference I finally decided to jump to the other side. I will no longer use any text editor or IDE for programming and will force myself to use vim exclusively. I also decided to use tmux instead of relying on the guake terminal for more awesomeness.

After two months, am I very pleased with the results: I now have my development environment set up using zshell, vim, and tmux and all the tools that I used to have before have been configured to work on vim. As I feel like I am years (maybe decades) late to the party, here is a simple guide I wrote to help people like me who want to dive head-first into vim and tmux.


This step is not really required to use Vim and Tmux, but it is recommended due to several improvements and plugins that you can use to improve your development environment.

In this guide, I will be using Ubuntu (or other Debian based systems) so I can be lazy and just install it using the package manager:

sudo apt-get install zsh

You can also check the version of the zshell installed to make sure its compatible with the plugins you want to use later on:

zsh --version

Once zshell has been installed, we will want to make it our default shell (instead of let’s say bash). This will make your system use zshell when you invoke the terminal or the command line.

chsh -s $(which zsh)

When you load zshell for the first time, it needs to be configured first and it will prompt you on how to do the initial configuration:

This is the Z Shell configuration function for new users,
You are seeing this message because you have no zsh startup files
(the files .zshenv, .zprofile, .zshrc, .zlogin in the directory
~). This function can help you with a few settings that should
make your use of the shell easier.

You can:

(q) Quit and do nothing. The function will be run again next time.

(0) Exit, creating the file ~/.zshrc containing just a comment.
That will prevent this function being run again.

(1) Continue to the main menu.

(2) Populate your ~/.zshrc with the configuration recommended
by the system administrator and exit (you will need to edit
the file by hand, if so desired).

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