Introduction to YAML¶

Experi uses the YAML file format for the input file since it has widespread use and support and the format is simple for a human to parse. From the perspective of a python developer, YAML is a method of specifying python data structures in a text file. A key construct of the YAML file is the mapping of a key to a value, like a python dictionary. Also like a python dictionary the mapping uses the colon

key: value

All keys have to be strings, although values can be a range of types. Values that look like a string, will become python strings, values that are integers will become python integers, and values that are floats will become python floats. A value can also be itself a mapping

key:
  value1: 1
  value2: 2
  value3: 3
  value4: 4

where the above example is the same as the python data structure

{'"key"': {"value1": 1, "value2": 2, "value3": 3, "value4": 4}}

YAML also supports using lists as values, which are denoted with bullet points

key:
  - 1
  - 2
  - 3
  - 4

where the value is now the python list [1, 2, 3, 4]. The python list syntax is another way to specify a list in a YAML file with the example below having the same value as the example above

key: [1, 2, 3 4]

The final feature of YAML files I will highlight here is the specification of long strings, which are particularly useful when writing long bash commands. To create a long single line string, start the string with the > character.

key: >
  A long string
  written over
  multiple lines

which will have no newline characters inserted. This is so much better than having to end line in bash with a \. To include the newlines in the string, you can instead use the | symbol

key: |
  Line 1
  Line 2
  Line 3
  END

which includes a newline character after each number.

The examples presented should be enough to get started using Experi. The following resources are recommended for further reading