abstract base class (abc) adapter pattern class adapter don' repeat yourself duck typing implementation mail_sender py object parting shots problem send_email py separation of concern users csv file barracks builder pattern abstraction anti-patterns basic_form_generator py cleaned_html_dictionary_form_ generator py course correct deliberate practice focus giants graphical library/machine-learning setup html_dictionary_form_generator py html_form_generator py - oop_html_form_generator py rapid feedback loop vincileonardo da widgets and interfaces chain of responsibility pattern authentication headers response object functions - implementation middleware print function - python (see pythonic implementationsingle responsibility principle wsgi server clone(method closures command pattern commands execute(method function definition implementation invoker macros multi-level undo stack multiplication receiver relevant parameters turtle composite pattern (cwessel badenhorst badenhorstpractical python design patterns