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In the life of a developer it often happens that you get assigned to an already existing software project, programmed by other developers. It can happen that this project is not maintained anymore by other developers.
I find it particularly difficult to get started on an existing project which has no active developers anymore because I don't know where to "dive in". We have for example a project which is not documented and there are no developers maintaining it. I got assigned to implement some features into this software. I got only the git repository link along my tasks. (The application is terminal-based and written in Python, but that doesn't matter)
What are the common practices to do when getting an existing project if nobody can help you? I can't ask the former developers anymore because they don't work at the company anymore.
How should I find out how the application works? I tried finding out what it actually does by installing it and trying out different commands (trial and error) but that takes a really long time. I search for a more straightforward solution for this case.