List index out of range when using more than one at the same time

Question

I'm trying to achieve an updating plot of random numbers, just as a learning exercise (which I can then pass real data).

I have written the following code, with the hope of ending up with a list of tuples (time and random number) which I can then split out and pass as axis to maplotlib.

def local_db_monitor(increment=10):
    import datetime
    import time
    import random
    import matplotlib
    import matplotlib.pyplot as plt
    import matplotlib.dates as mdates
    import pylab as pl

    time_list = []

    while True:
        now = datetime.datetime.utcnow().strftime('%H:%M:%S')
        rand_number = random.randint(1,100)

        time_rand = (now, rand_number)

        if len(time_list) >= increment:
            time_list.pop(0)
            time_list.append(time_rand)
        else:
            time_list.append(time_rand)

        items = zip(*time_list)

        x_val = list(items)[0]
        y_val = list(items)[1]

        print(x_val, y_val)

        # plt.plot(x_val, y_val)

        time.sleep(0.5) 

local_db_monitor()

The problem I'm having is with separating the list of tuples. I can get just the dates, or just the random numbers, but both indexes can't seem to be used at the same time.

<ipython-input-119-e33785849b16> in local_db_monitor(increment)
     39 
     40         x_val = list(items)[0]
---> 41         y_val = list(items)[1]
     42 
     43         print(x_val)
IndexError: list index out of range

Can someone please help me to understand what's going on here. I'm using iPython/Python 3.

Answer 1

You are trying to index a zip object, in python 3 zip returns an iterator, you need to call list on items if you want to index it:

items = list(zip(*time_list))

Or use next(items) :

items = zip(*time_list)
x_val, y_val = next(items),next(items)