How to implement cross-platform file locking in Python without extra dependencies

Concurrent writes from multiple processes to the same file can cause data corruption, making inter-process file locking a necessary safeguard. Python's standard library offers two incompatible APIs for this: fcntl on Unix-like systems and msvcrt on Windows, requiring platform-specific handling. On Unix, fcntl.flock() applies an advisory lock on the entire file, while Windows' msvcrt.locking() locks an explicit byte range within a file. Developers can unify both approaches in a single codebase using a sys.platform branch, importing each module only within its relevant code path to avoid import errors on the other platform. This technique eliminates the need for third-party packages like filelock, which is particularly useful when minimizing dependencies in desktop app distributions built with tools like PyInstaller.