YTE - A YAML template engine with Python expressions

YTE is a template engine for YAML format that utilizes the YAML structure in combination with Python expressions for enabling to dynamically build YAML documents.

Syntax

The key idea of YTE is to rely on the YAML structure to enable conditionals, loops and other arbitrary Python expressions to dynamically render YAML files. Python expressions are thereby declared by prepending them with a ? anywhere in the YAML. Any such value will be automatically evaluated by YTE, yielding plain YAML as a result. Importantly, YTE templates are still valid YAML files (for YAML, the ? expressions are just strings).

Examples

?if True:
  foo: 1
?elif False:
  bar: 2
?else:
  bar: 1

?for i in range(2):
  ?f"key{i}": 1
  ?if i == 1:
      foo: True

?if True:
  - a
  - b

- foo
- bar
- ?if True:
    baz
  ?else:
    bar

Usage

Command line interface

YTE comes with a command line interface. To render any YTE template, just issue

yte < the-template.yaml > the-rendered-version.yaml

Python API

Alternatively, you can invoke YTE via its Python API:

from yte import process_yaml

# set some variables as a Python dictionary
variables = ...

# render a string and obtain the result as a Python dict
result = process_yaml("""
?for i in range(10):
  - ?f"item-{i}"
""", variables=variables)

# render a file and obtain the result as a Python dict
with open("the-template.yaml", "r") as template:
    result = process_yaml(template, variables=variables)

# render a file and write the result as valid YAML
with open("the-template.yaml", "r") as template, open("the-rendered-version.yaml", "w") as outfile:
    result = process_yaml(template, outfile=outfile, variables=variables)