What are Split and Join (Python strings)?

In short

split breaks a string into a list of smaller strings at a separator, and join puts a list of strings together into one string with a separator between them.

In simple words

"a,b,c".split(",") gives ['a', 'b', 'c']. With no argument, split() breaks at any run of spaces. "-".join(["a", "b", "c"]) gives 'a-b-c'. The separator is written first in join, then the list. Both are used for cleaning data, such as turning a line of a file into numbers.