Why prefer 'with open()' over manual close()

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Accepted Answer

File objects implement the context manager protocol (__enter__ and __exit__). When the 'with' block exits - whether normally or via an exception - __exit__ calls close() for you. Without 'with', a manual f.close() after a read that raises an exception is simply never reached. The file stays open, holding an OS file descriptor, until the garbage collector eventually reclaims the object. In a long-running process or tight loop this causes descriptor leaks that can hit the OS limit (ulimit -n, typically 1024 or 4096). The rule is simple: every open() belongs inside a 'with' block.