I quantopified a class for tracking margins I worked on in zipline a while ago since it's difficult to write code that can be cut/pasted between the two.

It keeps a dict of position margins and the portfolio margin. It logs the data nice and pretty for you too, Enjoy!

import pandas as pd


class Margins(object):  
    '''  
    Calculates portfolio minimum margin requirement and  
    keeps a dict of the requirement for each position.  
    '''

    def __init__(self, context, data, day_trader=False):  
        self.initial_margin = 25000.0 if day_trader else 2000.0  
        self.position_margins = {}  
        for stock in data.keys():  
            self.position_margins[stock] = \  
                self.position_requirement(context.portfolio.positions[stock])  
        self.requirement = sum(self.position_margins.values())

    def position_requirement(self, position):  
        amount = position.amount  
        last_sale_price = position.last_sale_price  
        if amount >= 0:  
            req = .25 * amount * last_sale_price  
        else:  
            if last_sale_price < 5:  
                req = max(2.5 * amount, abs(amount * last_sale_price))  
            else:  
                req = max(5 * amount, abs(0.3 * amount * last_sale_price))  
        return req

    def __repr__(self):  
        template = "\nSymbol  Requirement\n{position_margins}\nMargin Requirement: {req}"  
        return template.format(  
            position_margins=pd.Series(  
                {i.symbol : self.position_margins[i]  
                 for i in self.position_margins}),  
            req=self.requirement)

    def __getitem__(self, item):  
        return self.position_margins[item]