'Place a batch market order for multiple assets.
Parameters
share_counts : pd.Series[Asset -> int]
Map from asset to number of shares to order for that asset.
Returns
order_ids : pd.Index[str]
Index of ids for newly-created orders.'

@api_method
@expect_types(share_counts=pd.Series)
@expect_dtypes(share_counts=int64_dtype)
def batch_market_order(self, share_counts):

    style = MarketOrder()
    order_args = [(asset, amount, style) for (asset, amount) in iteritems(share_counts) if amount]
    return self.blotter.batch_order(order_args)
