python-tips

Tips for using Python

1. Manage python versions wiyth pyenv

Note

pyenv only works on Mac or Linux. On Windows you can use the official py launcher.

See the user manual for pyenv:

pyenv --help

See a list of available versions:

pyenv install --list

Filter to only "3.11":

pyenv install --list | grep 3.11

Install a specific version:

pyenv install 3.11.7

You can install multiple versions and switch between them.

pyenv install 3.12.1

Select a specific Python version:

pyenv global 3.12.1  # globally in the shell
pyenv local 3.11.7   # locally in the current folder

Check the path to python interpreter

pyenv which python

2. Manage project python dependencies with poetry

Lookup manual pages with --help. See all commands with list:

poetry --help
poetry list

Create a poetry project:

poetry init

This will add a pyproject.toml file in the current folder.

Define dependecies in the toml file

Add project main dependencies, e.g. cognite sdk, pandas, and pydantic:

[tool.poetry.dependencies]
python = "^3.11.0"
cognite-sdk = "^7.52.3"
pandas = "^2.2.1"
pydantic = "^2.6.0"

Dependency specification syntax: poetry docs.

To be able to use a jupyter notebook install the following development dependencies:

[tool.poetry.group.dev.dependencies]
ipykernel = "*"
jupyter = "*"

Create a virtual environment with the selected pyenv interpreter

# set the local python version
pyenv local 3.11.7
# save the interpreter path to a variable
SELECTED_PY_PATH=$(pyenv which python)
poetry env use "$SELECTED_PY_PATH"

This will create a virtual environment based on the selected pyenv environment.

You can check the environment:

poetry env info

It will print a table with virtual env info and base. You will need the executable path from the virtual env to set up the Python path in the code editor later.

You can easily get this path with the command:

poetry env info | awk '/^Executable/{print $2}' | head -1

This command prints the info, then uses awk cli tool to find all lines that start with "Executable" string, outputs the second column (assuming space separated data), then takes only the first row using head.

Set the python interpreter in VS Code

Open the current folder in VS Code.

code .

Open the command palette (CMD + P). Start typing "Python: Select Interpreter". You should see the command highlighted. Tap the Enter key. Select "Enter interpreter path". Insert the python executable path that we got in the previous step from poetry env info. .

Now your editor should correctly highlight the code and. You may need to restart VS Code before it takes effect.

Install dependencies

poetry install

This will install the dpendencies from the lock file (if available) or based on the pyporject.toml and then create a lock file.

You can update dependenices if new versions matching the version requirment spec are available.

poetry update

Run python code

You need to use the correct python interpreter so that all the dependencies are found correctly. poetry run uses the correct virtual environment.

poetry run python demo_script.py

Or you can active the virtual environment first and the run the python script:

poetry shell

python demo_script.py