Safe string formatter

safe_format.py

class SafeFormat(string.Formatter):
    '''String formatting class that won't throw errors for usused/unfound args/kwargs.

    Values that can't be retrieved are returned in their original '{keyname}' string
    to allow for another round for .format()'ing

    Example
    -------
    >>> safe_format = SafeFormat().format
    >>>  log_str = 'the {color} dog jumped over the {animal}'

    # Pretend that it takes a lot of processing power to get the animal value,
    # so we'll partially build it ahead of time and will add the animal later.
    # This lets us log the string without having all the values.
    >>> my_str = safe_format(log_str, color='brown')  # 'the brown dog jumped over the {animal}'

    # Later ...
    >>> final_str = my_str.format(animal='cow')       # 'the brown dog jumped over the cow'
    '''
    def get_value(self, key, args, kwds):
        try:
            return super(SafeFormat, self).get_value(key, args, kwds)
        except (IndexError, KeyError):
            return '{%s}' % key