Python - rulebook

Fortunately or not, Python is unavoidable. So we need some rules to keep ourselves sane while using it.

XDG and home dir

First, let's remove the clutter:

• Create $XDG_CONFIG_HOME/python/startup.py and add the following code:

  import atexit
  import os
  import readline
  
  cachedir = os.getenv("XDG_CONFIG_HOME")
  histdir = ""
  if cachedir == "":
      cachedir = os.path.expanduser("~")
      histdir = os.path.join(cachedir, ".config", "python")
  else:
      histdir = os.path.join(cachedir, "python")
  
  os.makedirs(histdir, exist_ok=True)
  histfile = os.path.join(histdir, "history")
  
  hist_len = 0
  
  try:
      readline.read_history_file(histfile)
      hist_len = readline.get_current_history_length()
  except FileNotFoundError:
      open(histfile, 'wb').close()
  
  
  def save(prev_hist_len, histfile):
      new_hist_len = readline.get_current_history_length()
      readline.set_history_length(-1)
      readline.append_history_file(new_hist_len - prev_hist_len, histfile)
  
  
  atexit.register(save, hist_len, histfile)

• Add (or export) PYTHONSTARTUP variable, i.e. export PYTHONSTARTUP="$XDG_CONFIG_HOME"/python/startup.py .
• Create the history file at $XDG_CACHE_HOME/python/history .
• Reload the environment (logout should do).

Virtual environments

You must use virtual environments for all your python development. It is not optional.

$ python -m venv env
$ source env/bin/activate.fish # depending on the shell of choice
$ pip install number # e.g.
$ pip freeze > requirements.txt # to list all dependencies and their version into a file
$ pip install -r requirements.txt # to install all required dependencies

Note April 10, 2025 You should probably use uv.

This is it for today. I hope you find this guide useful. As per usual, if you find any errors, or if you have some additional (important) tips to share, send me a mail at luka [at] ljudi [dot] org. Cheers!