Tag Archives: Unit Testing

Some weird things from Python 3 that you may not know

Last Update: 2021-09-29 18:12 IST

You can find those bizarre things and more in my book Python 3 Combat Guide.

I’m not talking about the wonderful things, like how big can the Integers be, but about the bizarre things that may ruin your day.

What sums 0.1 + 0.1 + 0.1 in Python?

0.3?

Wrong answer.

A bit of humor

Well, to be honest the computer was wrong. They way programming languages handle the Floats tend to be less than ideal.

Floats

Maybe you know JavaScript and its famous NaN (Not a number).

You are probably sure that Python is much more exact than that…

…well, until you do a big operation with Floats, like:

10.0**304 * 10.0**50 

and

It returns infinite

I see your infinite and I add one :)

However If we try to define a number too big directly it will return OverflowError:

Please note Integers are handled in a much more robust cooler way:

Negative floats

Ok. What happens if we define a number with a negative power, like 10 ** -300 ?

And if we go somewhere a bit more far? Like 10 ** -329

It returns 0.0

Ups!

I mention in my books why is better to work with Integers, and in fact most of the eCommerces, banks and APIs work with Integers. For example, if the amount in USD 10.00 they send multiplied by 100, so they will send 1000. All the actor know that they have to divide by 2.

Breaking the language innocently

I mentioned always that I use the MT Notation, the prefix notation I invented, inspired by the Hungarian Notation and by an amazing C++ programmer I worked with in Volkswagen and in la caixa (now caixabank), that passed away many years ago.

Well, that system of prefixes will name a variable with a prefix for its type.

It’s very useful and also prevents the next weird thing from Python.

Imagine a Junior wants to print a String and they put in a variable. And unfortunately they call this variable print. Well…

print = "Hello World!"
print("That will hurt")

Observe the output of this and try not to scream:

Variables and Functions named equally

Well, most of languages are able to differentiate a function, with its parenthesis, from a variable.

The way Python does it hurts my coder heart:

Another good reason to use MT Notation for the variables, and for taking seriously doing Unit Testing and giving a chance to using getters and setters and class Constructor for implementing limits and sanitation.

Nested Loops

This will work in Python, it doesn’t work in other languages (but please never do it).

for i in range(3):
    print("First Loop", i)
    for i in range(4):
        print("Second Loop", i)

The code will not crash by overwriting i used in the first loop, but the new i will mask the first variable.

And please, name variables properly.

Import… once?

Imports are imported only once. Even if different files imported do import the same file.

So don’t have code in the middle of them, outside functions/classes, unless you’re really know what you’re doing.

Define functions first, and execute code after if __name__ == “__main__”:

Take a look at this code:

def first_function():
    print("Inside first function")
    second_function()

first_function()

def second_function():
    print("Inside second function")

Well, this will crash as Python executes the code from top to bottom, and when it gets to first_function() it will attempt to call second_function() which has not been read by Python yet. This example will throw an error.

You’ll get an error like:

Inside first function
Traceback (most recent call last):
  File "/home/carles/Desktop/code/carles/python_combat_guide/src/structure_dont_do_this.py", line 14, in <module>
    first_function()
  File "/home/carles/Desktop/code/carles/python_combat_guide/src/structure_dont_do_this.py", line 12, in first_function
    second_function()
NameError: name 'second_function' is not defined

Process finished with exit code 1

Add your code at the bottom always, under:

if __name__ == "__main__":
    main()

The code inside this if will only be executed if you directly call this code as main file, but will not be executed if you import this file from another one.

You don’t have this problem with classes in Python, as they are defined first, completely read, and then you instantiate or use them. To avoid messing and creating bugs, have the imports always on the top of your file.

A base Dockerfile for my Jenkins deployments

So I share with you my base Jenkins Dockerfile, so you can spawn a new Jenkins for your projects.

The Dockerfile installs Ubuntu 20.04 LTS as base image and add the required packages to run jenkins but also Development and Testing tools to use inside the Container to run Unit Testing on your code, for example. So you don’t need external Servers, for instance.

You will need 3 files:

  • Dockerfile
  • docker_run_jenkins.sh
  • requirements.txt

The requirements.txt file contains your PIP3 dependencies. In my case I only have pytest version 4.6.9 which is the default installed with Ubuntu 20.04, however, this way, I enforce that this and not any posterior version will be installed.

File requirements.txt:

pytest==4.6.9

The file docker_run_jenkins.txt start Jenkins when the Container is run and it will wait until the initial Admin password is generated and then it will display it.

File docker_run_jenkins.sh:

#!/bin/bash

echo "Starting Jenkins..."

service jenkins start

echo "Configure jenkins in http://127.0.0.1:8080"

s_JENKINS_PASSWORD_FILE="/var/lib/jenkins/secrets/initialAdminPassword"

i_PASSWORD_PRINTED=0

while [ true ];
do
    sleep 1
    if [ $i_PASSWORD_PRINTED -eq 1 ];
    then
        # We are nice with multitasking
        sleep 60
        continue
    fi

    if [ ! -f "$s_JENKINS_PASSWORD_FILE" ];
    then
        echo "File $s_FILE_ORIGIN does not exist"
    else
        echo "Password for Admin is:"
        cat $s_JENKINS_PASSWORD_FILE
        i_PASSWORD_PRINTED=1
    fi
done

That file has the objective to show you the default admin password, but you don’t need to do that, you can just start a shell into the Container and check manually by yourself.

However I added it to make it easier for you.

And finally you have the Dockerfile:

FROM ubuntu:20.04

LABEL Author="Carles Mateo" \
      Email="jenkins@carlesmateo.com" \
      MAINTAINER="Carles Mateo"

# Build this file with:
# sudo docker build -f Dockerfile -t jenkins:base .
# Run detached:
# sudo docker run --name jenkins_base -d -p 8080:8080 jenkins:base
# Run seeing the password:
# sudo docker run --name jenkins_base -p 8080:8080 -i -t jenkins:base
# After you CTRL + C you will continue with:
# sudo docker start
# To debug:
# sudo docker run --name jenkins_base -p 8080:8080 -i -t jenkins:base /bin/bash

ARG DEBIAN_FRONTEND=noninteractive

ENV SERVICE jenkins

RUN set -ex

RUN echo "Creating directories and copying code" \
    && mkdir -p /opt/${SERVICE}

COPY requirements.txt \
    docker_run_jenkins.sh \
    /opt/${SERVICE}/

# Java with Ubuntu 20.04 LST is 11, which is compatible with Jenkins.
RUN apt update \
    && apt install -y default-jdk \
    && apt install -y wget curl gnupg2 \
    && apt install -y git \
    && apt install -y python3 python3.8-venv python3-pip \
    && apt install -y python3-dev libsasl2-dev libldap2-dev libssl-dev \
    && apt install -y python3-venv \
    && apt install -y python3-pytest \
    && apt install -y sshpass \
    && wget -qO - https://pkg.jenkins.io/debian-stable/jenkins.io.key | apt-key add - \
    && echo "deb http://pkg.jenkins.io/debian-stable binary/" > /etc/apt/sources.list.d/jenkins.list \
    && apt update \
    && apt -y install jenkins \
    && apt-get clean

RUN echo "Setting work directory and listening port"
WORKDIR /opt/${SERVICE}

RUN chmod +x docker_run_jenkins.sh

RUN pip3 install --upgrade pip \
    && pip3 install -r requirements.txt


EXPOSE 8080


ENTRYPOINT ["./docker_run_jenkins.sh"]

Build the Container

docker build -f Dockerfile -t jenkins:base .

Run the Container displaying the password

sudo docker run --name jenkins_base -p 8080:8080 -i -t jenkins:base

You need this password for starting the configuration process through the web.

Visit http://127.0.0.1:8080 to configure Jenkins.

Configure as usual

Resuming after CTRL + C

After you configured it, on the terminal, press CTRL + C.

And continue, detached, by running:

sudo docker start jenkins_base

The image is 1.2GB in size, and will allow you to run Python3, Virtual Environments, Unit Testing with pytest and has Java 11 (not all versions of Java are compatible with Jenkins), use sshpass to access other Servers via SSH with Username and Password…

A live session refactoring and adding Unit Testing to my Python3 project cmemgzip

I refactor and add unit testing to my actual project cmemgzip while I comment every step so you can learn the whys and the reasoning.

Open video in full screen with max 1080 quality, in order to see the code clearly.

Update 2021-03-03: I added a third part. I’m tired but still is worth watching.