Matplotlib Wind Barb plotting issues

I have some code below, I am basically trying to plot wind barbs on a sounding plot

import urllib
import matplotlib.pyplot as plt
%matplotlib inline

def read_sounding(url):
    pressure=[]
    altitude=[]
    temp    =[]
    lines  = urllib.request.urlopen(url).readlines()
    for line in lines[10:76]:
        entries = line.decode("utf-8").split(" ")
        columns=[]
        for entry in entries:
            if len(entry) > 1: columns.append(entry)
        if len(columns) > 2: # otherwise data not available
            pressure.append(float(columns[0]))
            altitude.append(float(columns[1]))
            temp.append(float(columns[2]))
    return(pressure,altitude,temp)
def read_wind(url):
    wind = []
    lines  = urllib.request.urlopen(url).readlines()
    for line in lines[10:76]:
        entries = line.decode("utf-8").split(" ")
        columns=[]
        for entry in entries:
            if len(entry) > 1: columns.append(entry)
        if len(columns) > 2: # otherwise data not available
            wind.append(float(columns[7]))
    return(wind)
def location(url):
    lines  = urllib.request.urlopen(url).readlines()
    lon=lines[81] # longitude
    lat=lines[80] # latitude
    lon=float(lon.decode("utf-8").split(":")[1])
    lat=float(lat.decode("utf-8").split(":")[1])
    return(lat,lon)   

if __name__ == '__main__':
    url    = 'http://weather.uwyo.edu/cgi-bin/sounding?region=naconf&TYPE=TEXT%3ALIST&YEAR=2005&MONTH=07&FROM=0812&TO=0812&STNM=72469'
    p,h,t=read_sounding(url)
    lat,lon=location(url)
    W= read_wind(url)
    plt.plot(t,h,'o--')
    #print(W)
    plt.barbs(W)
    plt.xlabel("temperature [C]")
    plt.ylabel("altitude [m]")
    plt.title('lat='+str(lat)+' lon='+str(lon))

the error I get is in the line plt.barb and its an error that says "pop from empty list" even though when I print the returned value I have a list with numbers in it. I am able to produce a sounding plot for temperature but I need to add wind barbs to it. The link in the main function has all of the data in columns. The exact error is "Index Error: pop from empty list"