Strange output in matplotlib

Question

Can someone explain why I get this strange output when running this code:

import matplotlib.pyplot as plt
import numpy as np
def x_y():
    return np.random.randint(9999, size=1000), np.random.randint(9999, size=1000)
plt.plot(x_y())
plt.show()

The output:

Answer 1

Your data is a tuple of two 1000 length arrays.

def x_y():
    return np.random.randint(9999, size=1000), np.random.randint(9999, size=1000)
xy = x_y()
print(len(xy))
# > 2
print(xy[0].shape)
# > (1000,)

Let's read pyplot's documentation:

plot(y) # plot y using x as index array 0..N-1

Thus pyplot will plot a line between (0, xy[0][i]) and (1, xy[1][i]), for i in range(1000).

You probably try to do this:

plt.plot(*x_y())

This time, it will plot 1000 points joined by lines: (xy[0][i], xy[1][i]) for i in range 1000.

Yet, the lines don't represent anything here. Therefore you probably want to see individual points:

plt.scatter(*x_y())

Answer 2

Your function x_y is returning a tuple, assigning each element to a variable gives the correct output.

import matplotlib.pyplot as plt
import numpy as np
def x_y():
    return np.random.randint(9999, size=1000), np.random.randint(9999, size=1000)
x, y = x_y()
plt.plot(x, y)
plt.show()