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What is YAML? A Complete Beginner‘s Guide

YAML (YAML Ain‘t Markup Language) is a human-readable data serialization language that is commonly used for configuration files, data exchange between programs, data storage, and more. In this comprehensive beginner‘s guide, we will cover:

Brief History of YAML

YAML was created in 2001 by Clark Evans, Ingy döt Net, and Oren Ben-Kiki as a human-friendly alternative to XML and other heavyweight data serialization formats. The goal was to design an easy-to-read format that could be used for common tasks like configuration files, localization, data storage, and data exchange between programs.

Over the years, YAML has gained widespread adoption due to its focus on human readability and support for flexible data types. Major programs and frameworks like Kubernetes, Ansible, Ruby on Rails, and more use YAML for configuration and data storage.

Benefits of YAML

Here are some of the main benefits that YAML provides over other data serialization options:

  • Readability – YAML prioritizes human readability with minimal syntax. Data structures are indented using spaces rather than heavy bracket syntax.
  • Comments – Supports inline comments for additional context.
  • Flexible data types – Supports a range of data types out-of-the-box: strings, integers, floats, booleans, null.
  • Language independence – Can be used from any programming language.
  • Hierarchical data – Supports complex nested data structures.

YAML Syntax Basics

At a high level, a YAML document contains mappings (think key-value pairs), sequences (think lists or arrays), and scalars (strings, numbers, etc).

Here is a simple example with some key YAML components:

# This entire document is a mapping
website:
  # Mappings can be nested 
  owner:
    # Scalars are basic values like strings, numbers
    name: John Smith 
    age: 30
  # Sequences are denoted by a leading - 
  categories:
    - blogging 
    - programming
    - web development

Let‘s break this example down:

  • The top-level website key denotes the start of a mapping.
  • Mappings use a simple key: value syntax – the owner and categories keys in this example.
  • The owner mapping contains nested name and age mappings.
  • The name and age values are basic YAML scalars.
  • Sequences like the categories list use leading – characters.

In addition to these basics, YAML supports advanced functionality like anchors/aliases for avoiding duplication and multiline strings for improved readability.

Data Types

As mentioned above, YAML has a flexible set of supported data types out-of-the-box:

  • Strings – Plain unformatted text. Can use single or double quotes.
  • Integers – Whole numbers like 10 or -300.
  • Floats – Decimals like 3.14159.
  • Booleans – true or false values.
  • Null – Null or nil value representing no value.
  • Mappings – Key-value store, like dictionaries in Python or hashes in Ruby.
  • Sequences – Lists or arrays.

These core data types allow developers to store a wide variety of hierarchical configuration data and application state in an easy-to-read YAML format.

Usage in Programming Languages

Since YAML aims to be a human-friendly data format that is programming language-independent, it has become widely supported across all major languages:

  • Python – pyyaml library
  • JavaScript – js-yaml library
  • Ruby – built-in YAML support
  • Java – snakeyaml library
  • C#/.NET – YamlDotNet library

This makes YAML an ideal language-agnostic format for configuration, data files, and more. Developers can leverage YAML from any environment.

Here is a brief code example for parsing a YAML file in Python using pyyaml:

import yaml

with open(‘data.yaml‘) as f:
data = yaml.load(f, Loader=yaml.FullLoader)


print(data)

Example Applications

Here are some of the most common use cases and applications where YAML shines:

Configuration Files

Many programs leverage YAML for configuration since it is easy to read and edit as a human:

  • Web frameworks like Ruby on Rails
  • DevOps tools like Kubernetes, Ansible, Salt
  • CircleCI, Travis CI continuous integration

Data Storage & Transfer

The flexibility to support complex data hierarchies makes YAML great for structured data:

  • APIs often accept/return YAML payloads
  • YAML works well as a database serialization format
  • Data pipelines serialize state in YAML

Localization

Human readability makes YAML a common choice for localization and translations:

  • Mobile apps use YAML instead of rigid XML
  • Games can store dialog options and text in YAML files

Compare YAML to JSON and XML

The two most common alternatives to YAML are JSON and XML. Here‘s a quick comparison:

  • JSON is simpler than YAML but supports fewer data types.
  • XML provides namespacing but is overly verbose for many applications.
  • YAML strikes a nice balance – more human-friendly than JSON with fewer syntax headaches than XML.

The optimal choice depends on your specific application. YAML hits the sweet spot for use cases where human maintainability is a priority.

Limitations of YAML

While excellent for many applications, YAML does come with some limitations to consider:

  • Not ideal for complex transactional data (better suited for configurations)
  • Less strict error handling than JSON/XML
  • Advanced features introduce complexity that can reduce human readability

YAML is designed to be simple to read and write for humans but remains a structured serialization language. It inherits some downsides when data models become overly complex.

Learn More

I hope this guide gave you a comprehensive YAML overview! Here are additional resources to learn more:

  • Official YAML Documentation – https://yaml.org/spec/
  • Wikipedia Overview – https://en.wikipedia.org/wiki/YAML
  • YAML Tutorials:
    • Python – https://rollout.io/blog/yaml-tutorial-everything-you-need-get-started/
    • JavaScript – https://www.digitalocean.com/community/tutorials/js-yaml-js

Let me know if you have any other YAML questions!

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