Matplotlib returning a plot object

I think the error is pretty self-explanatory. There is no such thing as pyplot.plt, or similar. plt is the quasi-standard abbreviated form of pyplot when being imported, i.e., import matplotlib.pyplot as plt.

Concerning the problem, the first approach, return axarr is the most versatile one. You get an axis, or an array of axes, and can plot to it.

The code may look like:

def plot_signal(x,y, ..., **kwargs):
    # Skipping a lot of other complexity here
    f, ax = plt.subplots(figsize=fig_size)
    ax.plot(x,y, ...)
    # further stuff
    return ax

ax = plot_signal(x,y, ...)
ax.plot(x2, y2, ...)
plt.show()