dict .keys() and .values()
Implicit `.keys()` fails for Dart, Julia & Rust.
```py
def implicit_keys():
    CODES = {"KEY": 1}
    return "KEY" in CODES
```

Only Julia can handle explicit `.keys()`
```py
def explicit_keys():
    CODES = {"KEY": 1}
    return "KEY" in CODES.keys()
```