The code in the gym program is a copy of your code in the coffee bar. And copying code is a bad thing. Once you have two separate copies of a piece of code, then changes need to be applied in two places. So how do we avoid copying code?
The secret is to break your programs into smaller pieces of code called modules. What's a module? It's just a file containing code the computer can run. Every Python program you've written so far has been a single module.
But most programs you'll write will probably be split across many, many modules. And writing modular code is important because modules can be shared between programs.
If you separate out the code that saves the transactions to a file and store it in a new module called transactions . py, that module can be shared by both programs. If you then ever need to change the code in transactions . py, both programs will pick up the changes automatically.
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