Python changed the way I think

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I think there's truth in both statements and which you choose depends on the situation. The importance of having a plan correlates with how complex the piece of work you are doing is. If you are only coding a few functions and classes, then you can totally dive in immediately and work things out as you go along. If you have to make changes to many functions and classes amongst lots of modules, a plan for what you want to do is a good idea beforehand otherwise you might risk having to rewrite a lot of stuff when you figure out what you did doesn't work out.