Python data struct dict group by values

gistfile1.txt

from collections import defaultdict 

def group_by_owners(files):
    # Grouping dictionary keys by value 
    res = defaultdict(list)
    for key, val in files.items(): 
        res[val].append(key) 
    return res

if __name__ == "__main__":    
    files = {
        'Input.txt': 'Randy',
        'Code.py': 'Stan',
        'Output.txt': 'Randy'
    }   
    print(group_by_owners(files))