robust_string_format.py

class FormatDict(dict): 
    def __missing__(self, key): 
        return '{{{}}}'.format(key)

      
def format_string(string, context: dict) -> str:
    """
    Format string without KeyError if key is not present in dict.

    >>> format_string('Oh, hi {first_name} {last_name}', {'first_name': 'Mark'})                                                                                           
    'Oh, hi Mark {last_name}'
    """
    return string.format_map(FormatDict(**context))