Btw: The name "read_dict" [1] as well as its docstring say exactly the opposite of what it does. It acts as a "save_dict". Maybe that can be fixed on the go ...

The docstring

""" [...]
All types held in the dictionary are converted to strings during
reading, including section names, option names and keys. [...]
"""

actually implies what is my proposal here: Convert arguments to str during lookup as well.

```
    def __getitem__(self, key):
        if key != self.default_section and not self.has_section(key):
            raise KeyError(key)
        return self._proxies[key]
```

to

```
    def __getitem__(self, key):

        try: key = str(key)
        except (WhateverError, IsRelevantHereError): raise KeyError(key)

        if key != self.default_section and not self.has_section(key):
            raise KeyError(key)
        return self._proxies[key]
```

[1] https://github.com/python/cpython/blob/3.7/Lib/configparser.py