NanoDano's blog

Introduction

Working with files and directories is a common task when developing in Python. Let's look at several useful tools and methods for working with files and directories.

If you work with files, you might also find my tutorial Working with Binary Data in Python useful.

Among the popular operating systems, they have all standardized on using standard input, standard output, and standard error with file desciptors 0, 1, and 2 respectively. This allows you to pipe the inputs and outputs to different locations. Let's look at how to utilize standard input, output, and error in Python.

To learn more about piping, redirection, stdin, stdout, and stderr in general, see my tutorial STDIN, STDOUT, STDERR, Piping, and Redirecting.

When processing command line arguments in Python, you have a few options available:

• sys.argv - a raw list of arguments passed to the Python interpreter
• argparse - Python's standard package for argument parsing (replaces getopt and optparse)
• fileinput.input() - A special function, similar to Ruby's ARGF, that returns the lines of input from standard input or from the list of filenames provided as arguments.
• docopt - A third-party package that uses the docstring as documentation and configuration for arg parsing
• click - A third-party package that uses decorators to map command arguments

Let's look at examples of each option.

In Linux and MacOS environments, you can terminate standard input by outputting EOF (end of file) using the CTRL-D keyboard shortcut. In Windows, the CTRL-D key combination does not do the same. Lets look at how to accomplish this in Windows Command Prompt or Powershell.

There are a few ways to get user keyboard input from the terminal:

• Using the input() function
• using sys.stdin directly
• Getting a password with getpass.getpass()

Let's look at each one now.

Python has a built-in package for converting Python objects to and from JSON strings. We will look at how to load JSON from a string or a file, and dump a Python object to a JSON string or file. We will also look at how to minify the output and save space, or make it more human readable with ordering and indentation.

A common task when working with systems is to create directories. There can be times when you need to create a directory several layers deep. The normal mkdir commands only let you create a single level at a time. This example will show you how to create multiple directory levels at once, the equivalent of running mkdir -p in the Bash shell.

jpackage is a new tool with JDK 14 that generates native system installers for distributing your appliction. It will create .msi for Windows, .dmg for Mac, and .deb or .rpm for Linux distrubtions. This is ideal for GUI applications. This guide will demonstrate how to use this tool to create system native installers for your applications.

The third-party cryptography package in Python provides tools to encrypt byte using a key. The same key that encrypts is used to decrypt, which is why they call it symmetric encryption. Fernet is an encryption spec that utilizes AES-128 under the hood with HMAC and some other additions. If you need to encrypt and decrypt some data using Python, this is a very easy way to do it.

Before Java 9 and Project Jigsaw, you would have to package the entire monolithic Java Runtime Environment (JRE) to distribute your application with an embedded JRE runtime. This took up a lot of space. Now, you can generate your own custom runtime with only the modules you want to keep the size of the final package smaller.

You can think of a runtime image as another name for a Java runtime environment (JRE). When you create a custom runtime, you are generating a new JRE that only includes the modules you want. You can exclude core java modules that you don't need and you can include custom modules that you wrote. They will all be "baked in" to the runtime.

If you are familiar with Python Virtual Environments, it is similar to that. It is a directory that contains an isolated Java environment with only the specific dependencies needed that will not conflict with other isolated runtimes.

After following this guide, you will understand how to use jlink to create runtime images with only the modules you want. You should also know how to add custom modules including third-party modules like JavaFX.