@external
def __init__(_beneficiary: address, _auction_start: uint256, _bidding_time: uint256):
self.beneficiary = _beneficiary
self.auctionStart = _auction_start # auction start time can be in the past, present or future
self.auctionEnd = self.auctionStart + _bidding_time
assert block.timestamp < self.auctionEnd # auction end time should be in the future