PermissionError: Permission denied

Python code developed on macOS or Linux frequently encounters Permissionerror on Windows because of path separator differences, case sensitivity, shell availability, and how Windows handles scripts. The most impactful differences: Windows uses backslash (\) as the path separator — use pathlib.Path or os.path.join() rather than string concatenation. Windows is case-insensitive for paths, so import MyModule and import mymodule both work on Windows but only one works on Linux. os.system() or subprocess commands that call bash, grep, sed, or awk fail on Windows unless run inside WSL2 or Git Bash. Python scripts without a shebang line need python script.py explicitly — not ./script.py. For PowerShell users, the activation script for venv is .venv\Scripts\Activate.ps1, but PowerShell's execution policy may block it — run Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser once to allow signed local scripts.