How to solve AssertionError when running backtest on zipline

I'm working through the book Trading Evolved by Andreas Clenow and am running into an AssertionError when trying to run the code for the first backtest on zipilne. I am new to python and zipline and appreciate any guidance on how to solve this error. Here is the source code taken from the book's website:

# This ensures that our graphs will be shown properly in the notebook.
%matplotlib inline

#Import pandas as pd

import pandas as pd

# Import Zipline functions that we need
from zipline import run_algorithm
from zipline.api import order_target_percent, symbol

# Import date and time zone libraries
from datetime import datetime
import pytz

# Import visualization
import matplotlib.pyplot as plt


def initialize(context):
    # Which stock to trade
    context.stock = symbol('AAPL')

    # Moving average window
    context.index_average_window = 100

def handle_data(context, data):
    # Request history for the stock
    equities_hist = data.history(context.stock, "close", 
                                 context.index_average_window, "1d")

    # Check if price is above moving average
    if equities_hist[-1] > equities_hist.mean():
        stock_weight = 1.0
    else:
        stock_weight = 0.0

    # Place order
    order_target_percent(context.stock, stock_weight)

def analyze(context, perf):
    fig = plt.figure(figsize=(12, 8))

    # First chart
    ax = fig.add_subplot(311)
    ax.set_title('Strategy Results')
    ax.semilogy(perf['portfolio_value'], linestyle='-', 
                label='Equity Curve', linewidth=3.0)
    ax.legend()
    ax.grid(False)

    # Second chart
    ax = fig.add_subplot(312)
    ax.plot(perf['gross_leverage'], 
            label='Exposure', linestyle='-', linewidth=1.0)
    ax.legend()
    ax.grid(True)

    # Third chart
    ax = fig.add_subplot(313)
    ax.plot(perf['returns'], label='Returns', linestyle='-.', linewidth=1.0)
    ax.legend()
    ax.grid(True)

# Set start and end date
start_date = datetime(1996, 1, 1, tzinfo=pytz.UTC)
end_date = datetime(2018, 12, 31, tzinfo=pytz.UTC)

# Fire off the backtest
results = run_algorithm(
    start=start_date, 
    end=end_date, 
    initialize=initialize, 
    analyze=analyze, 
    handle_data=handle_data, 
    capital_base=10000, 
    data_frequency = 'daily', bundle='quandl' 
)

After running this I get the below error.

---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-23-0e4e6c712343> in <module>()
     75     handle_data=handle_data,
     76     capital_base=10000,
---> 77     data_frequency = 'daily', bundle='quandl'
     78 ) 
     79 

/opt/anaconda3/envs/zipenv/lib/python3.5/site-packages/zipline/utils/run_algo.py in run_algorithm(start, end, initialize, capital_base, handle_data, before_trading_start, analyze, data_frequency, bundle, bundle_timestamp, trading_calendar, metrics_set, benchmark_returns, default_extension, extensions, strict_extensions, environ, blotter)
    391         environ=environ,
    392         blotter=blotter,
--> 393         benchmark_spec=benchmark_spec,
    394     )
    395 

/opt/anaconda3/envs/zipenv/lib/python3.5/site-packages/zipline/utils/run_algo.py in _run(handle_data, initialize, before_trading_start, analyze, algofile, algotext, defines, data_frequency, capital_base, bundle, bundle_timestamp, start, end, output, trading_calendar, print_algo, metrics_set, local_namespace, environ, blotter, benchmark_spec)
    200             trading_calendar=trading_calendar,
    201             capital_base=capital_base,
--> 202             data_frequency=data_frequency,
    203         ),
    204         metrics_set=metrics_set,

/opt/anaconda3/envs/zipenv/lib/python3.5/site-packages/zipline/finance/trading.py in __init__(self, start_session, end_session, trading_calendar, capital_base, emission_rate, data_frequency, arena)
     36                  arena='backtest'):
     37 
---> 38         assert type(start_session) == pd.Timestamp
     39         assert type(end_session) == pd.Timestamp
     40 

AssertionError:

Appreciate any help on how to solve this.

Solution

Your current start_date and end_date variable should produce:

# Set start and end date
start_date = datetime(1996, 1, 1, tzinfo=pytz.UTC)
end_date = datetime(2018, 12, 31, tzinfo=pytz.UTC)
type(start_date)

out [1]:

datetime.datetime

Please try:-

Solution [1]:

# Set start and end date
start_date = pd.Timestamp('1996-1-1', tz='utc')
end_date = pd.Timestamp('2018-12-31', tz='utc')
type(start_date)

out [1]:

pandas._libs.tslib.Timestamp

Solution [2]:

# Set start and end date
start_date = pd.to_datetime('1996-1-1', utc=True)
end_date = pd.to_datetime('2018-12-31', utc=True)
type(start_date)

out [2]:

pandas._libs.tslib.Timestamp