Beyond a single file.
WHEN TO SPLIT
When a file becomes hard to navigate When parts are reusable When distinct responsibilities exist
HOW TO DIVIDE
By responsibility, not by type.
WHAT THAT MEANS
Group code that changes together.
WHAT A TYPICAL STRUCTURE SEPARATES
Entry point Core logic Data access Configuration Utilities
WHY SEPARATE DATA ACCESS
So logic can be tested without a database.
WHAT TO KEEP AT THE TOP LEVEL
As little as possible.
Code at module level runs on import, which surprises people.
WHAT TO PUT BEHIND THE STANDARD ENTRY CHECK
Anything that should run only when the file is executed directly.
WHY
So the module can be imported without executing it.
WHAT TO AVOID
Circular dependencies between modules One module knowing too much about others A utilities module that becomes a dumping ground
WHAT TO REVIEW
Whether the structure still reflects what the program does.
