data = [('a', 1), ('b', 2), ('b', 3), ('c', 4), ('c', 5)]
result = {}
for key, value in data:
result.setdefault(key, []).append(value)
for key, values in result.items():
print(key, values)
ZGF0YSA9IFsoJ2EnLCAxKSwgKCdiJywgMiksICgnYicsIDMpLCAoJ2MnLCA0KSwgKCdjJywgNSldCnJlc3VsdCA9IHt9CmZvciBrZXksIHZhbHVlIGluIGRhdGE6CiAgICByZXN1bHQuc2V0ZGVmYXVsdChrZXksIFtdKS5hcHBlbmQodmFsdWUpCmZvciBrZXksIHZhbHVlcyBpbiByZXN1bHQuaXRlbXMoKToKICAgIHByaW50KGtleSwgdmFsdWVzKQ==