problems with Python Django NSException

I am working on a project using Django and Python and I am trying to plot a simple graph using matplotlib and I keep getting the error

uncaught exception of type NSException

Python also crashed after that. I am using mac if that helps.

Matplotlib version '3.1.0'

I have already tried using the most simple graphs but still the problem persists.

This is my code in the views.py file

def get_svg(request):
    t = np.arange(0.0, 2.0, 0.01)
    s = 1 + np.sin(2 * np.pi * t)

    fig, ax = plt.subplots()
    ax.plot(t, s)

    ax.set(xlabel='time (s)', ylabel='voltage (mV)',
               title='Sample')
    ax.grid()

    response = HttpResponse(content_type = 'image/png')
    canvas = FigureCanvasAgg(fig)
    canvas.print_png(response)
    return response

This is the error message I get:

Terminating app due to uncaught exception 'NSInternalInconsistencyException',
  reason: 'NSWindow drag regions should only be invalidated on the Main Thread!'
  libc++abi.dylib: terminating with uncaught exception of type NSException