removing duplicates from a sequence while maintaining order

example2.py

# example2.py
#
# Remove duplicate entries from a sequence while keeping order

def dedupe(items, key=None):
    seen = set()
    for item in items:
        val = item if key is None else key(item)
        if val not in seen:
            yield item
            seen.add(val)

if __name__ == '__main__':
    a = [ 
        {'x': 2, 'y': 3},
        {'x': 1, 'y': 4},
        {'x': 2, 'y': 3},
        {'x': 2, 'y': 3},
        {'x': 10, 'y': 15}
        ]
    print(a)
    print(list(dedupe(a, key=lambda a: (a['x'],a['y']))))