Python's Mypy--Advanced Usage

Your Weekly Newsletter [view in browser »]( Want to stay more up to date on all things open source? Follow us on [Twitter](. [Python]( Python's Mypy--Advanced Usage Reuven M. Lerner - June 24, 2019 Mypy can check more than simple Python types. In [my last article](, I introduced Mypy, a package that enforces type checking in Python programs. Python itself is, and always will remain, a dynamically typed language. However, Python 3 supports "annotations", a feature that allows you to attach an object to variables, function parameters and function return values. These annotations are ignored by Python itself, but they can be used by external tools. Mypy is one such tool, and it's an increasingly popular one. The idea is that you run Mypy on your code before running it. Mypy looks at your code and makes sure that your annotations correspond with actual usage. In that sense, it's far stricter than Python itself, but that's the whole point. In [my last article](, I covered some basic uses for Mypy. Here, I want to expand upon those basics and show how Mypy really digs deeply into type definitions, allowing you to describe your code in a way that lets you be more confident of its stability. Type Inference Consider the following code: x: int = 5 x = 'abc' print(x) This first defines the variable x, giving it a type annotation of int. It also assigns it to the integer 5. On the next line, it assigns x the string abc. And on the third line, it prints the value of x. [read article]( [Blinky]( FreeDOS's Linux Roots Jim Hall - June 27, 2019 On June 29, 2019, the FreeDOS Project turns 25 years old. That's a major milestone for any open-source software project! In honor of this anniversary, Jim Hall shares this look at how FreeDOS got started and describes its Linux roots. [Read Article]( [Podcast]( 2.0 - Episode 21: From Mac to Linux Katherine Druckman and Doc Searls talk to Linux Journal Editor at Large, Petros Koutoupis, about moving from Mac to Linux. [Listen Now]( [Rust Logo]( Getting Started with Rust: Working with Files and Doing File I/O Mihalis Tsoukalos - June 20, 2019 How to develop command-line utilities in Rust. This article demonstrates how to perform basic file and file I/O operations in Rust, and also introduces Rust's ownership concept and the Cargo tool. [read article]( On-demand webinar brought to you by Twistlock [Watch Now »]( [Twistlock Webinar]( in case you missed [Security Lock] Understanding Public Key Infrastructure and X.509 Certificates Jeff Woods - June 21, 2019 An introduction to PKI, TLS and X.509, from the ground up. [Read Article »]( [Command Line] Without a GUI--How to Live Entirely in a Terminal Bryan Lunduke - June 28, 2019 Sure, it may be hard, but it is possible to give up graphical interfaces entirely—even in 2019. [Read article »]( upcoming events [Open Source Software Conference]( July 15, 2019 - July 18, 2019 Portland, Oregon USA [Open Source Summit North America]( August 23, 2019 - August 24, 2019 San Diego, California USA [All Things Open]( October 13, 2019 - October 15, 2019 Raleigh, North Carolina USA [PIA]( [Storix Software]( [Twistlock]( [Technologic Systems]( Subscribe to Linux Journal for only $2.88 an issue! [Subscribe Now »]( [Renew Now »]( You are receiving this email because you signed up to receive newsletters from Linux Journal. You can [update your preferences]( or [unsubscribe]( from this list. Copyright © 2019 Linux Journal LLC, All rights reserved. Mailing address: 9597 Jones Rd, #331 Houston, TX 77065