import matplotlib.pyplot as plt
import numpy as np

def func3(x, ):
    return (1 - x/2 + x**5 + y**3) * np.exp(-x**2 - y**2)


# make these smaller to increase the resolution
dx, dy = 0.05, 0.05

x = np.arange(-3.0, 3.0001, dx)
y = np.arange(-3.0, 3.0001, dy)
X, Y = np.meshgrid(x, y)

Z = func3(X, Y)

# fails
plt.pcolor(X, Y, list(Z))
# plt.pcolor(X, Y, Z)  # works