Network automation to screen-scraping devices is primarily concerned with gathering output from show commands and with making configuration changes.
Netmiko aims to accomplish both of these operations and to do it across a very broad set of platforms. It seeks to do this while abstracting away low-level state control (i.e. eliminate low-level regex pattern matching to the extent practical).
Nornir is an automation framework written in python to be used with python. Most automation frameworks hide the language they are written in by using some cumbersome pseudo-language which usually is almost Turing complete, but lacks tooling to debug and troubleshoot. Integrating with other systems is also usually quite hard as they usually have complex APIs if any at all. Some of the other common problems of those pseudo-languages is that are usually quite bad at dealing with data and re-usability is limited.
Nornir aims to solve those problems by providing a pure python framework. Just imagine Nornir as the Flask of automation. Nornir will take care of dealing with the inventory where you have your host information, it will take care of dispatching the tasks to your devices and will provide a common framework to write “plugins”.
NAPALM (Network Automation and Programmability Abstraction Layer with Multivendor support) is a Python library that implements a set of functions to interact with different network device Operating Systems using a unified API.
NAPALM supports several methods to connect to the devices, to manipulate configurations or to retrieve data.