configparser interface implicitly converts all objects to str (read_dict [sic] on line 724 of "Lib/configparser.py") while saving but not while lookup (__getitem__ on line 956).

MWE:

```
config = configparser.ConfigParser()
config[123] = {}
print(config[123])
```
~> KeyError: 123

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

> 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 name `read_dict` is correct, it reads from the dict given as parameter and changing the name would break existing code.

I opened a new PR with the change to convert keys to strings in __getitem__, I did not wrap `key = str(key)` in a try-except as it's not done in read_dict(). This way both __getitem__ and read_dict() will fail the same way.

Other methods do not convert key to string too.

What is a use case for having a non-string section name?

Other methods validate explicitly their arguments with _validate_value_types for example.

Here it raises KeyError which does not seem to be the appropriate exception. ConfigParser implementing the mapping protocol it seems weird to me to have

    >>> a = 123
    >>> config[a] = {}
    >>> config[a]
    KeyError: 123

I would have prefered a TypeError to be raised on __setitem__ but this is now documented behavior.

This is indeed inconsistent, but it's a minor issue that has been this way for a long time and is easily worked around. IMO changing it would create more problems than leaving it as-is.

IMO we should at most clarify in the docs.

> IMO we should at most clarify in the docs.

This makes sense, I will update my PR tomorrow.