Python at the CPG

Python at the CPG#

The CPG is mostly a Python shop! We strongly recommend using virtual environments (over conda) to manage Python.

We try to stay relatively up-to-date, most of our tools use Python 3.11 (with a few rare 3.8 exceptions), some are using 3.10 or 3.12. This can be super confusing!

Managing Python versions#

We strongly recommend using pyenv to manage versions of Python. This makes it really easy to install and manage multiple versions:

brew install pyenv

You will need to run the following to set up pyenv on zsh. Make sure to source the .zshrc file before running pyenv in the next step:

echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.zshrc
echo '[[ -d $PYENV_ROOT/bin ]] && export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.zshrc
echo 'eval "$(pyenv init -)"' >> ~/.zshrc

pyenv install 3.11.12
pyenv global 3.11.12

Named virtual environments#

If you like named virtual environments (rather than many env/ directories in your repos), take inspiration from this snippet you could add to your .zshrc file:

export VIRTUALENV_DIR="$HOME/.venv"

if command -v pyenv 1>/dev/null 2>&1; then
  eval "$(pyenv init -)"
fi

function venv() {
  if test -f "$VIRTUALENV_DIR/$@/bin/activate"; then
    source $VIRTUALENV_DIR/$@/bin/activate
  else
    # have to use (pyenv which python3) otherwise old conda could take over
    virtualenv -p $(pyenv which python3) $VIRTUALENV_DIR/$@/ && source $VIRTUALENV_DIR/$@/bin/activate
  fi
}
function activate() {
  source $VIRTUALENV_DIR/$@/bin/activate
}
alias venvlist="ls $VIRTUALENV_DIR && echo 'You can activate one of these virtualenvs with: activate <env>'"

# allow autocomplete of `activate <name>`
_activate_completion() {
    local cur_word="${COMP_WORDS[COMP_CWORD]}"
    COMPREPLY=($(compgen -W "$(ls $VIRTUALENV_DIR | grep "^$cur_word")" -- "$cur_word"))
}
complete -F _activate_completion activate

Typing#

Since the release of PEP 604 in Python 3.10, we are able to use type annotations such as:

x: str | None = None

which is preferred over:

from typing import Optional
x: Optional[str] = None

due to some caveats with the use of Optional but also to keep the codebase simpler, and less reliant on the use of additional modules.

Visual Studio Code#

See Code editors for more information on configuring Python in VSCode.

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