from typing import Set
import string


def get_format_keys(format_string: str) -> Set[str]:
    """
    Extract format keys from a formet-ready string.

    ```python
    keys = get_format_keys('key: {key} {value}')
    keys # ['key', 'value']
    ```

    Arguments:
        format_string -- A format-ready string.

    Returns:
        A set of format keys.
    """
    result = set()
    formatter = string.Formatter()
    for _, key, _, _ in formatter.parse(format_string):
        if key:
            result.add(key)

    return result