Depends how you organize your code. You can just decentralize the code by writing 1 class and let that be 1 file, and then you just import that class into another file. So each separate "chapter" of the code can be in a different file, much easier to manage.

Certainly cramming everything into 1 file and then having 1 extra space somwhere that can mess up things is risky.

So for code longer than 2 A4 papers I think the best thing to do is just use multiple files, especially if you code alone and have no bug-tester friend.