How do I print something whenever two lines meet in matplotlib with Python?

Heres my code:

import matplotlib.pyplot as plt
import pandas as pd
import urllib

API = 'http://api.example.com'
data = urllib.request.urlopen(API)
df = pd.DataFrame(data)

x = df['x'].tolist()
y1 = df['y1'].tolist()
y2 = df['y2'].tolist()

fig = plt.figure()
ax1 = plt.subplot2grid((1,1), (0,0))
ax1.plot(x, y1, label='y1')
ax1.plot(x, y2, label='y2')
plt.show()

So basically I've plotted two lines:

ax1.plot(x, y1, label='y1')
ax1.plot(x, y2, label='y2')

Assuming that the chart is live and updating. I want python to print a warning message whenever the lines meet, with another condition that it will only print a warning message for 100 times.

Here's what I got so far:

I defined the warning_message function to print a warning message.

def warning_message():
    print("Warning!")

I've also done the other condition wherein it will only print a warning message for 100 times.

count = 100
while count != '0':
    warning_message()
    count -= 1

What's missing inside this while loop is the condition that it will only print the warning message whenever the lines meet. Does anyone know how do it? :D

Solution

Since the lines share the same x data, it's rather easy to compare their y data. Simply asking whether y2 > y1 is enough.

import numpy as np

y1 = np.array([1,2,3])
y2 = np.array([0,1,3.1])

if np.any(y2>y1):
    print("warning")

In order to make this work in your script, don't use .tolist() but keep the data as numpy arrays, i.e. y1 = df['y1'].values.

It seems some more guidance is needed. So to check for every possible case, y2 comes from above y1, or from below y1, you may do the following:

import numpy as np

y1 = np.array([1,2,3])
y2 = np.array([0,1,2.9])+1

c = y2>y1
if (np.any(c) and not np.all(c)) or (np.any(~c) and not np.all(~c)):
    print("warning")

if np.all(c) or np.all(~c):
    #reset counter here
    pass