Created : 12th May tags : #python 🐍

Python Virtual Environments

It began when i tried to install altdns in Kali but couldn’t as it relied on Python 2 (even though Kali defaults to python2). Naturally, i wanted a permanent fix for this problem.

What is the Problem?

I want to be able to run / install a python program irrespective of what python version is installed on my pc.

Solution

We use pyenv to use different versions of python along with virtual environments options for each project.

Explain in Detail

First we look at how to install pyenv and then go to my workflow.

Installing pyenv

1.Installing Python ( For ubuntu or Kali )

kali@kali:~$ sudo apt install -y 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 python3-openssl git

kali@kali:~$ curl https://pyenv.run | bash

2.Depending upon the shell, add following lines to your .bashrc or .zshrc

# Here my default shell is zsh
kali@kali:~$ echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.zshrc 
kali@kali:~$ echo 'export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.zshrc 
# Note the slight change here
kali@kali:~$ echo -e 'if command -v pyenv 1>/dev/null 2>&1; then\n eval "$(pyenv init --path)"\nfi' >> ~/.zshrc 
kali@kali:~$ echo 'eval "$(pyenv virtualenv-init -)"' >> ~/.zshrc

3.Restart the Shell

kali@kali:~$ exec $SHELL

Note: Restart if using GUI or log off and log in again if using GUI

Now we have pyenv installed. We can check via pyenv versions

kali@kali:~$ pyenv versions
* system (set by /home/ubuntu/.pyenv/version)
  2.7.18
  
 # Install python 2.7.18 using below command
 kali@kali:~$ pyenv install 2.7.18       # Above we can see already done, so not installing here again
 ...

Now we have two options, first is to switch python version globally from system default (Python3) to Python 2.7.18 (that we installed now), but we won’t go to that route. Instead we will make virtualenvs, that use Python 2.

My Workflow

After Setting up pyenv and installing the desired python version. Lets make different version for different projects with help of virtuaenv. I’ll explain workflow with help of a use case.

Suppose i want to install altdns (requires python2). So i do the following

# Here i start with a fresh VM
kali@kali:~$ pyenv versions
* system (set by /home/kali/.pyenv/version)

kali@kali:~$ pyenv install 2.7.18 
Downloading Python-2.7.18.tar.xz...
-> https://www.python.org/ftp/python/2.7.18/Python-2.7.18.tar.xz
Installing Python-2.7.18...
Installed Python-2.7.18 to /home/kali/.pyenv/versions/2.7.18

kali@kali:~$ pyenv versions
* system (set by /home/kali/.pyenv/version)
  2.7.18

kali@kali:~$ mkdir tools                             
kali@kali:~$ cd tools

# Create project folder
kali@kali:~$ mkdir altdns && cd altdns

# Activate pyenv-virtualenv
kali@kali:~$ pyenv virtualenv 2.7.18 venv-altdns
kali@kali:~$ pyenv local venv-altdns && pyenv activate venv-altdns

(venv-altdns) kali@kali:~$       
# Changed directory and prompt goes away
kali@kali:~$ cd altdns 

# vevn automatically acitvated when chagned to the directory
(venv-altdns)  kali@kali:~$ pip install py-altdns  
...
# altdns installed and works
(venv-altdns) kali@kali:~$ altdns -h            
usage: altdns [-h] -i INPUT -o OUTPUT [-w WORDLIST] [-r] [-n] [-e]
              [-d DNSSERVER] [-s SAVE] [-t THREADS]

...

What we Achieved

Automatic switching between different python versions (depending on our current working directory).
Meanwhile, Virtualenvs (serving as isolated containers) give us power to use different python versions without conflicting with eachother.

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