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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_target(self, asset, target, limit_price=None, stop_price=None, style=None):
 """Place an order to adjust a position to a target number of shares. If the position doesn't already exist, this is equivalent to placing a new order. If the position does exist, this is equivalent to placing an order for the difference between the target number of shares and the current number of shares. Parameters asset : Asset The asset that this order is for. target : int The desired number of shares of ``asset``. 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 ----- ``order_target`` does not take into account any open orders. For example: .. code-block:: python order_target(sid(0), 10) order_target(sid(0), 10) This code will result in 20 shares of ``sid(0)`` because the first call to ``order_target`` will not have been filled when the second ``order_target`` call is made. 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_target_percent` :func:`zipline.api.order_target_value` """

        if not self._can_order_asset(asset):
            return None

        amount = self._calculate_order_target_amount(asset, target)
        return self.order(asset, amount,
                          limit_price=limit_price,
                          stop_price=stop_price,
                          style=style)