Your own exceptions

Built-in exceptions like ValueError and KeyError are generic. They don't tell you whether the problem is in your config or somewhere else, which is why libraries define their own exceptions as a family: a base class that inherits from Exception, and a subclass for each case. Calling code can then catch exactly what it can handle: except ConfigError catches the whole family, and except MissingKeyError catches just one case.

When you turn one of Python's own errors, like KeyError, into one from your family, write raise MissingKeyError("port") from err. The original error is kept in __cause__, and both appear together in the traceback instead of the cause getting lost.

The problem with the current code is that except Exception swallows every error, even your own bugs. A missing key, an invalid value and a typo in the key name all return port 8000 without a word, and you won't find out the config is broken until the program has reached your users.