code: def partial_format(target, **kwargs):
    
    output = target[:]
  
    for tag, var in re.findall(r'(\{(.*?)\})', output):
      root = var.split('.')[0]  # dot notation
      root = root.split('[')[0]  # dict notation
      if root in kwargs:
        output = output.replace(tag, tag.format(**{root: kwargs[root]}))
  
    return output
docs: Formats a string without requiring all values to be present.
  
    This function allows substitutions to be gradually made in several steps
    rather than all at once.  Similar to string.Template.safe_substitute.