If the dict included both str and int keys, sorted returns this error :
TypeError: '<' not supported between instances of 'int' and 'str'

It is a little bit problematic when used with default library behavior, as jsonify in Flask.

possible solution :
try:
    items = sorted(dct.items())
except(TypeError):
    items = sorted(dct.items(), key=lambda kv: str(kv[0]))

It's not clear what you suggest, but it is likely better to alert the user that their keys have mismatched types than to suppress it by default.

Perhaps alongside the `sort_keys` argument, you would like a parameter that gets passed into `sorted()` when the items are sorted?

Perhaps an additional argument, or if sort_keys is a callable, use that as the `key` argument to sorted?

``` 
strange = {"1":"one", 2:"ii"}
json.dumps(strange, sort_keys=True, key=str)
json.dumps(strange, sort_keys=str)
# {"1": "one", 2: "ii"}
```

This is an exact duplicate of #25457.