Live plotting from CSV file with matplotlib.animation - Data drawn to first entry error - csv

Question

I am attempting to plot data from a sensor that is continuously being written to a CSV file. While successful in creating a live plot, each new data entry creates an additional line that extends to the first data entry. See Below:
The Python 3.4 Script:
import matplotlib.pyplot as plt
import matplotlib.animation as animation
import time
import datetime as dt
import csv
fig = plt.figure()
ax1 = fig.add_subplot(1,1,1)
x=[] ; y1=[]; y2=[]; y3=[]
def animate(i):
with open( 'data_log.csv', 'r') as csvfile:
alphasensefile = csv.reader(csvfile, delimiter = ',')
next(alphasensefile, None)
next(alphasensefile, None)
next(alphasensefile, None)
for column in alphasensefile:
a = dt.datetime.strptime((column[0]), '%H:%M:%S')
x.append((a))
y1.append(column[1])
y2.append(column[2])
y3.append(column[3])
ax1.clear()
ax1.plot(x,y1)
ani = animation.FuncAnimation(fig, animate, interval=1000)
plt.show()
Running this script collects sensor data and records it to a CSV file. Every data entry recorded live from that start draws an additional line that goes to the first data entry point. Like so:
if I open the file while the sensor is not recording, only the last data entry is linked to the first point like so:
Data is recorded to the CSV file like so:
PM Data Recorded: 23 03 2018
Time, PM 1, PM 2.5, PM 10
16:12:10, 0.1173, 0.1802, 3.2022
Any thoughts to why this is occurring?

Answer 1

FIX:
After a while playing around with the code, i changed the code to:
import matplotlib.pyplot as plt
import matplotlib.animation as animation
import matplotlib.dates as matdate
from matplotlib import style
import time
import datetime as dt
import csv
style.use('bmh')
fig = plt.figure()
ax = fig.add_subplot(1,1,1)
def animate(i):
csvfile = open( 'data_log.csv', 'r+')
alphasensefile = csv.reader(csvfile, delimiter = ',')
next(alphasensefile, None)
next(alphasensefile, None)
next(alphasensefile, None)
x=[] ; y1=[]; y2=[]; y3=[]
for column in alphasensefile:
a = dt.datetime.strptime((column[0]), '%H:%M:%S')
x.append((a))
y1.append(column[1])
y2.append(column[2])
y3.append(column[3])
ax.clear()
ax.plot(x, y1, label = 'PM 1 ', linewidth=0.7)
ani = animation.FuncAnimation(fig, animate, interval=1000)
plt.show()
This plots the data live and smooth without issues.