Different ways to use Python

We present here different ways to run Python programs, from the most accessible to the most flexible.

In the first part of this training, we used JupyterLite to run Python directly in the browser — no installation required. This is convenient for learning, but a Python developer also needs to be able to run Python locally, understand which interpreter is active, and work efficiently from the terminal or an IDE.

This section walks through the main approaches: running scripts from the terminal, working interactively with IPython, editing code in an IDE, and using JupyterLab for notebook-style workflows.

Python: a language and some interpreters¶

Python is a programming language.

The most common way to execute Python code is to interpret it. Through misuse of language, one says that Python is an interpreted language (like Bash, Matlab, and in contrast with Fortran, C or C++). To interpret code, we need an interpreter, i.e. a program parsing Python code and running computer instructions.

The interpreter is a program, which is somewhere is your computer. The program is associated with a command (typically python or python3) that one can use in the terminal without giving the full path.

Most of the time, users of Python software don’t need to know where is the interpreter. However, as a Python developer, it is usually good to have an idea about which interpreter is used.

Exercise 1

Open a terminal. Depending on your OS, run the following commands:

Windows

macOS and Linux

Get-Command python
Get-Command py

The results depend on your computer state...

On Linux, you should have the system Python (a command python3 corresponding to a file /usr/bin/python3). On Linux, when no virtual environment is activated, there is usually no python command.

Execute a script with the command `python3`¶

Exercise 2

Run a script with python3 (helloworld.py is just a text file):

python3 src/common/examples/helloworld.py

From the terminal, change the current directory with cd src/common/examples and rerun the file with just

python3 helloworld.py

Open the file with an editor (for example VSCode that can be launched from the terminal with code .), change the name in the code and rerun the file from the terminal.

Work interactively with IPython¶

The command ipython launches the program IPython, which is used for interactive python.

Exercise 3

In IPython, you can execute a first interactive instruction:

2 + 2

4

3 / 4

0.75

Run the script from IPython.

%run helloworld.py

Hello world
My name is Pierre

In the file helloworld.py, a variable called name is defined.

print(name)

Pierre

Help on an object can be displayed with the question mark (try it):

name?

Try to type name. and to press on tab... The tab key is used to tell you how what you typed can be completed.
Try to use the top and bottom arrows...

Python in an IDE (Visual Studio Code)¶

Launch the application Visual Studio Code, a lightweight IDE (Integrated Development Environment).

VSCode is first a very good code editor with:

syntax coloring,
code analysis powered by pyflakes and pylint,
introspection capabilities such as code completion.

For this training we will mostly use this feature, but VSCode is actually much more than that.

Exercise 4 (Install VSCode extensions for Python)

Open the directory of this training with VSCode:

cd py-edu-fr
code .

Install the following extensions via the Extensions panel (Ctrl+Shift+X / Cmd+Shift+X):

Python (look for ms-python) — language support, environment management, debugger
Ruff (charliermarsh) — fast linter and formatter

Python in the browser (JupyterLab)¶

Jupyter is a very powerful tool to present results (see these examples). For example, the presentations of this python training are made with Jupyter Notebooks.

Let us launch Jupyter Lab with the command:

jupyter-lab

This should start a server and maybe also open the corresponding application in your browser. If the application does not automatically starts, use one of the http addresses given in the terminal.