import numpy as np 
import matplotlib.pyplot as plt

x = []
y = []
v = []
with open('testdata.txt') as f:
    for line in f:
        a, b, c = line.strip().split()
        x.append(float(a))
        # y.append(float(b))
        v.append(float(c))

fig, ax = plt.subplots()
ax.plot(x, v)
plt.show()
# plt.savefig("main.png")