使用字典：
>>> data = [('Visa', 980.5), ('Rogers', 61.5), ('Visa', 215.0)]
>>> result = {}
>>> for card, value in data:
total = result.get(card, 0) + value
result[card] = total
>>> print result.items()
[('Visa': 1195.5), ('Rogers': 61.5)]
602392714
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