[Python] Linspace in numpy library

I want to draw 3d lines using Python. I used Matplotlib, but I have a problem with the linspace function, and Axes3D. I already included MatplotLib and numpy library to the project.

this is the code :

import matplotlib as mpl
from mpl_toolkits.mplot3d import Axes3D
import numpy as np
import matplotlib.pyplot as plt

mpl.rcParams['legend.fontsize'] = 10

fig = plt.figure()
ax = fig.gca(projection='3d')
theta = np.linspace(-4 * np.pi, 4 * np.pi, 100)
z = np.linspace(-2, 2, 100)
r = z**2 + 1
x = r * np.sin(theta)
y = r * np.cos(theta)
ax.plot(x, y, z, label='parametric curve')
ax.legend()

plt.show()


this picture will clarify the code bugs and the libraries: picture

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