Python

virtualenv -p python3 venv
. venv/bin/activate
pip install flake8 pytest black

Run with python file.py, test with pytest file.py. Format the code with black file.py. The flake8 install makes Elpy (the Emacs Python environment) lint code properly.

Information in this section is taken from this document.

The primary use of init.py is to initialize Python packages. The inclusion of the init.py file in a directory indicates to the Python interpreter that the directory should be treated like a Python package.

init_.py can be an empty file but it is often used to perform setup needed for the package(import things, load things into path, etc).

One common thing to do in your init.py is to import selected Classes, functions, etc into the package level so they can be convieniently imported from the package.

In our example above we can say that file.py has the Class File. So without anything in our init.py you would import with this syntax:

from package.file import File

However you can import File into your init.py to make it available at the package level:

# in your __init__.py
from file import File

# now import File from package
from package import File

Another thing to do is at the package level make subpackages/modules available with the all variable. When the interpeter sees an all variable defined in an init.py it imports the modules listed in the all variable when you do:

from package import *

all is a list containing the names of modules that you want to be imported with import * so looking at our above example again if we wanted to import the submodules in subpackage the all variable in subpackage/__init__.py would be:

__all__ = ['submodule1', 'submodule2']

With the all variable populated like that, when you perform

from subpackage import *

it would import submodule1 and submodule2.

See https://docs.python.org/3.0/whatsnew/3.0.html for specific information. Here's a list of changes that have affected me:

• Python 3 stores strings as Unicode by default, whereas Python 2 requires you to mark a string with a “u” if you want to store it as Unicode.
• The print statement has been replaced with the print() function.
• range() now behaves like xrange() used to behave, except it works with values of arbitrary size. The latter no longer exists.
• An expression like 1/2 returns a float. Use 1//2 to get the truncating behavior.
• Extended Iterable Unpacking. You can now write things like a, b, *rest = some_sequence. And even *rest, a = stuff. The rest object is always a (possibly empty) list; the right-hand side may be any iterable. Example: (a, *rest, b) = range(5). This sets This sets a to 0, b to 4, and rest to [1, 2, 3].
• Dictionary comprehensions
• Set literals. Set comprehensions are also supported.

Python 3.6 also adds formatted string literals or f-strings. See this page.

Information in this section is taken from the virtualenv docs.

virtualenv "creates an environment that has its own installation directories, that doesn't share libraries with other virtual env environments (and optionally doesn't access the globally installed libraries either)." An example of a time this utility is useful is when you have two applications that use different versions of a certain library.