So this is probably a dumb question, but I have now been searching for quite some time, and I haven't been able to figure out what they do even though I see them often in source-codes.
You won't see it in source code, it's probably documentation. It indicates an interactive session, and things typed into the 'interpreter' are marked with this. Output is shown without the arrows.
In fact, the python documentation often has a button >>>at the top right of example code to be able to hide the arrows (and output) so that you can copy and paste the code.
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