2.8 YAML

A .yml file is a file that uses the YAML format, which stands for “YAML Ain’t Markup Language” (a recursive acronym).

YAML (YAML Ain’t Markup Language) is a human-readable data serialization format. It’s commonly used for configuration files, data exchange between languages, and in applications where data readability and simplicity are important. Here’s a beginner’s overview of YAML:

What is YAML? §

1. Human-Readable Data Format: YAML is designed to be easy for humans to read and write. It emphasizes simplicity and readability, making it a popular choice for configuration files.

2. Data Serialization: It can represent data structures like lists (arrays), associative arrays (maps or dictionaries), and scalar values (strings, numbers, booleans).

3. Whitespace and Indentation Sensitive: YAML uses indentation (spaces) to denote structure, similar to how Python does. This makes the structure visually clear but also means that correct indentation is crucial.

4. Format: YAML files are saved with the .yml or .yaml extension.

Basic Syntax and How to Read/Write YAML: §

1. Scalars (Strings, Numbers, Booleans):

   • Strings don’t necessarily need quotes.
   • Numbers and Booleans are represented in standard formats.
   • Example:

     name: John Doe
     age: 30
     active: true

2. Lists (Arrays):

   • Represented with a hyphen and a space (- ) followed by list elements.
   • Example:

     hobbies:
       - Reading
       - Gaming
       - Coding

3. Associative Arrays (Maps, Dictionaries):

   • Key-value pairs are represented with a colon and a space.
   • Example:

     address:
       street: 123 Main St
       city: Anytown
       zip: 12345

4. Nested Structures:

   • Indentation is used to represent hierarchy.
   • Example:

     employee:
       name: John Doe
       job:
         title: Developer
         department: IT

5. Comments:

   • Begin with a #.
   • Example:

     # This is a comment
     name: John Doe

Best Practices: §

1. Indentation: Use spaces, not tabs, for indentation. The standard is 2 spaces for each level of indentation.

2. Consistency: Be consistent with your use of quotes and indentation levels.

3. Validation: Use a YAML validator to check your syntax, especially when you’re starting out.

4. Readability: Even though YAML is flexible with certain syntax (like quotes), prioritize readability.

Example YAML File: §

# Employee record
employee:
  name: John Doe
  age: 30
  position: Developer
  skills:
    - Java
    - Python
    - SQL
  address:
    street: 123 Main St
    city: Metropolis
    zip: 54321

In this example, we have a dictionary with an employee’s details, a list of skills, and a nested dictionary for the address.

Uses of YAML: §

• Configuration Files: Common in software applications and services. Examples include Docker Compose files, Kubernetes configuration files, and continuous integration setup files.
• Data Exchange: As a more readable alternative to JSON and XML in simple data exchange scenarios.

YAML is valued for its simplicity and human-centric design, making it a good choice for situations where configuration files are frequently accessed and edited by humans.