python -c

• To execute a single line or block of Python code.
• Provided as a string argument directly in the terminal, without requiring a separate script file.

requirements.txt

• Lists every external lib (dependency).
• Run pip install -r requirements.txt to read the file and auto downloads and installs everything on the list.

__init__.py

• __init__.py will treat the folder as a package (importable module).
• Hence, from backend.models.grid import Cell can work.
• Can just empty in the file if don't need any package-level setup code.

__pycache__

• Automatically created it when run any .py file.
• It stores compiled bytecode (.pyc files) so Python doesn't reparse the source code every time.
• Speed optimization.
• Never touch it, never commit it to git.

.pycache__/
└── constants.cpython-312.pyc   
// compiled version of constants.py