#!/usr/bin/env python3
from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure
import numpy as np

fig = Figure(figsize=(8,6))
canvas = FigureCanvas(fig)
ax = fig.add_subplot(1,1,1)
ax.set_yscale('log')          # <--- works fine without this line
ax.transData.transform((1,1)) # <--- exception thrown here

ax.transData.transform(np.array((1,1)).reshape(1,-1))