Python versions at Udacity

Most Nanodegree programs at Udacity will be (or are already) using Python 3 almost exclusively.

Why we're using Python 3

Jupyter is switching to Python 3 only
Python 2.7 is being retired
Python 3 has been out for almost 10 years, and there are very few dependencies (and none in this program) that are incompatible.

At this point, there are enough new features in Python 3 that it doesn't make much sense to stick with Python 2 unless you're working with old code. All new Python code should be written for version 3. Read more here .

The main breakage between Python 2 and 3

For the most part, Python 2 code will work with Python 3. Of course, most new features introduced with Python 3 versions won't be backwards compatible. The place where your Python 2 code will fail most often is the print statement.

For most of Python's history including Python 2, printing was done like so:

print "Hello", "world!"
> Hello world!

This was changed in Python 3 to a function.

print("Hello", "world!")
> Hello world!

The print function was back-ported to Python 2 in version 2.6 through the __future__ module:

    # In Python 2.6+
    from __future__ import print_function
    print("Hello", "world!")
    > Hello world!

The print statement doesn't work in Python 3. If you want to print something and have it work in both Python versions, you'll need to import print_function in your Python 2 code.