Python Introduction

Python Introduction#

Hello, World#

Let’s start by a simple “Hello, World” program. Put the following into a file hello.py:

print("Hello, World")

and then we can run it as:

python hello.py

This invokes the python interpreter, python, which runs the code in our file.

We can already see some similarities with C++:

  • print() is a function that takes arguments

  • "Hello, World" is a string.

but also some differences, perhaps the biggest of which is that there is no ``main`` function.

Using python#

Python is used not only for writing programs, but it is used interactively.

There are several ways we can work with python:

  • Writing scripts / programs in files ending with .py. For this we would use our editor to write the program and then run it via the python command, as we did above.

    Tip

    We can add the following line to our .emacs to have it automatically check our code as we write it (the same way we did with C++):

    (add-hook 'python-mode-hook 'flycheck-mode)

  • Interactively, using the interpreter as a REPL, just like we saw with Bash in our discussion The shell.

    • We can use the python, or ipython interpreter for this. These support command recall via the arrow keys and tab-completion.

    • We can use jupyter notebooks, which gives us a web-based environment for working with python, and can include code, plain text, output, and plots all in a single document (a notebook).

We will mostly work with just python, both interactively and for running scripts.

Tip

We can use python as a calculator just by doing typing

python

in our shell, and then typing math expressions (using much the same syntax as in C++), e.g., 1 + 2 * 5

Using the MathLab computers#

For most of what are a going to do, we can just use the python version that is the default on our computers (it is a bit old, but it’s okay). We can start the python interpreter just by doing:

python

When we need to install additionally libraries later, we can use the pip command.

Using portal / portal2#

The default version of python on portal / portal2 is python 3.9, which is quite old. We can run python 3.12 by using the command:

python3.12

you can install ipython with this version via:

pip3.12 install ipython

Then when you do

ipython

the ipython interpreter for python 3.12 will start up.

Using your own computer#

If you want to set up python on your own computer, I would recommend the Anaconda python distribution. This will install the latest python version and all of the libraries we typically need for scientific computing.

You can download the installer at https://www.anaconda.com/download/success?reg=skipped

Anaconda is available for Linux, Mac, and Windows, and is completely free.

Learning more#

There are lots of resources online for learning more about python: