Matplotlib - Fail to allocate bitmap

Basically I'm just running a for-loop that plots and saves a bunch of figures as PNG and when I'm up to like 25 figures to save in total I get this "Fail to allocate bitmap" error however I make sure to clear the axis, figure and figure window in between each one, so what gives?

Here's my code just in case:

def update_trade_graphs(instruments):
print('chokepoint 13')
for i in range(0, len(instruments)):
    if instruments[i].linked_trade is False:
        continue

    # Update variables
    bid = instruments[i].orderbook['bids'][0][0] if len(instruments[i].orderbook['bids']) > 0 else None
    ask = instruments[i].orderbook['asks'][0][0] if len(instruments[i].orderbook['asks']) > 0 else None

    trades[instruments[i].linked_trade].time_series.append(date2num(current_time_mark))
    trades[instruments[i].linked_trade].bid_prices.append(bid)
    trades[instruments[i].linked_trade].ask_prices.append(ask)

    for timespan in timespans_all:
        if timespan in trades[instruments[i].linked_trade].buy_targets:
            pass
        else:
            trades[instruments[i].linked_trade].buy_targets[timespan] = []

        trades[instruments[i].linked_trade].buy_targets[timespan].append(instruments[i].minmax[timespan][0])

        if timespan in trades[instruments[i].linked_trade].sell_targets:
            pass
        else:
            trades[instruments[i].linked_trade].sell_targets[timespan] = []

        trades[instruments[i].linked_trade].sell_targets[timespan].append(instruments[i].minmax[timespan][1])

    # Plot graph
    fig = plt.figure()
    ax1 = plt.subplot2grid((1, 1), (0, 0))

    for timespan in timespans_all:
        ax1.plot_date(trades[instruments[i].linked_trade].time_series,
                      trades[instruments[i].linked_trade].buy_targets[timespan], '-', label='Buy Target', color='c')
        ax1.plot_date(trades[instruments[i].linked_trade].time_series,
                      trades[instruments[i].linked_trade].sell_targets[timespan], '-', label='Sell Target',
                      color='m')

    ax1.plot_date(trades[instruments[i].linked_trade].time_series, trades[instruments[i].linked_trade].bid_prices,
                  '-', label='Bid', color='r')
    ax1.plot_date(trades[instruments[i].linked_trade].time_series, trades[instruments[i].linked_trade].ask_prices,
                  '-', label='Ask', color='b')

    ax1.axhline(trades[instruments[i].linked_trade].entry_price, linestyle=':', color='c')
    if trades[instruments[i].linked_trade].exit_price > 0:
        ax1.axhline(trades[instruments[i].linked_trade].exit_price, linestyle=':', color='m')

    for label in ax1.xaxis.get_ticklabels():
        label.set_rotation(90)
    ax1.grid(True)

    plt.xlabel('Date')
    plt.ylabel('Price')
    plt.title(trades[instruments[i].linked_trade].symbol)

    plt.subplots_adjust(left=0.09, bottom=0.23, right=0.94, top=0.95, wspace=0.2, hspace=0)

    plt.savefig('trade_{0}.png'.format(instruments[i].linked_trade))
    plt.close(fig)
    plt.clf()
    plt.cla()

from Matplotlib - Fail to allocate bitmap