Implementing an Interface for Reading Configuration from a YAML File for Yaydoc

Yaydoc reads configuration specified in a YAML file to set various options during the build process. This allows users to customize various properties of the build process. The current implementation for this was very basic. Basically it uses a pyYAML, a yaml parser for python to read the file and convert it to a python dictionary. From the dictionary we extracted values for various properties and converting them to strings using various heuristics such as converting True to ”true”, False to ”false”, a list to comma separated string and None to an empty string. Finally, we exported variables with those values.

Recently the entire code for this was rewritten using object-oriented paradigm. The motivation for this came from the fact that the implementation lacked certain features and also required some refactoring for long term readability. In the following paragraph, I have discussed the new implementation.

Firstly a Configuration class was created which basically wraps around a dictionary and provide certain utility methods. The primary difference is that the Configuration class allows dotted key access. This means that you can use the following syntax to access nested keys.

theme = conf[‘build.theme.name’]

The class provides another method connect which is used to connect environment variables with configuration values. This method also takes a dotted key but provides an extension on top of that to handle the case when a certain option can take multiple values. For example,

option: my_option

Or,

option:
  - my_option1
  - my_option2

To indicate that a certain config is of this type, you can specify a “@” character at the end of the key. Anything after the “@” character is assumed to be an attribute of each element within the list. Let’s see an example of this whole process.

build:
  subproject:
    - url: <url1>
  source: “doc”
    - url: <url2>

Now to extract all urls from the above file, we’d need to do the following

config.connect(‘SUBPROJECT_URLS’, ‘build.subproject@url’)

To extract sources, we’ll also use the default parameter as the source option is optional.

config.connect(‘SUBPROJECT_SOURCES’, build.subproject@source’, default=’docs’)

Finally, The Configuration object also provides a getenv method which reads all connection and serializes values to string according to the previously described heuristics. It then returns a dictionary of all environment variables which must be set.

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