For 3D plotting to work in Matplotlib, near the beginning of the first .py file you use to start your program, you must have imports in this order:
import matplotlib as mpl
from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt
If you try importing Axes3D in a later function that actually does the 3D plotting, it may give a runtime error.
If you feel you may use either function as an entry point, you can put the above 3 lines of code in both functions.