Refactor: remove code duplication

[sbrugman]

Parts of the API in the code contains substantial amounts of duplicated code. Examples are arguments and docstrings that are defined for multiple levels or nested functions. An example is the regenerate function.

Pylint can be used to detect these issues in part:

-   repo: https://github.com/pycqa/pylint
     rev: pylint-2.6.0
     hooks:
     -   id: pylint

Refactoring the code improves readability and maintainability.

Arguments can be passed via **kwargs, perhaps we would like to use docrep to propagate the docstrings.