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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def order_percent(self, asset, percent, limit_price=None, stop_price=None, style=None):
 """Place an order in the specified asset corresponding to the given percent of the current portfolio value. Parameters asset : Asset The asset that this order is for. percent : float The percentage of the portfolio value to allocate to ``asset``. This is specified as a decimal, for example: 0.50 means 50%. limit_price : float, optional The limit price for the order. stop_price : float, optional The stop price for the order. style : ExecutionStyle The execution style for the order. Returns ------- order_id : str The unique identifier for this order. Notes ----- See :func:`zipline.api.order` for more information about ``limit_price``, ``stop_price``, and ``style`` See Also -------- :class:`zipline.finance.execution.ExecutionStyle` :func:`zipline.api.order` :func:`zipline.api.order_value` """

        if not self._can_order_asset(asset):
            return None

        amount = self._calculate_order_percent_amount(asset, percent)
        return self.order(asset, amount,
                          limit_price=limit_price,
                          stop_price=stop_price,
                          style=style)