Set matplotlib legend markersize to a constant - python-3.x

Question

I'm making a diagram using matplotlib, and it has plt.Circles and plt.axvlines to represent different shapes. I need a legend to describe these shapes, but the problem is the legend marker (the image part), changes size depending on the input, which looks awful. How do I set the size to a constant?
fig = plt.figure(figsize=(6.4, 6), dpi=200, frameon=False)
ax = fig.gca()
# 3 Circles, they produce different sized legend markers
ax.add_patch(plt.Circle((0,0), radius=1, alpha=0.9, zorder=0, label="Circle"))
ax.add_patch(plt.Circle((-1,0), radius=0.05, color="y", label="Point on Circle"))
ax.add_patch(plt.Circle((1, 0), radius=0.05, color="k", label="Opposite Point on Circle"))
# A vertical line which produces a huge legend marker
ax.axvline(0, ymin=0.5-0.313, ymax=0.5+0.313, linewidth=12, zorder=1, c="g", label="Vertical Line")
ax.legend(loc=2)
ax.set_xlim(-2,1.2) # The figsize and limits are meant to preserve the circle's shape
ax.set_ylim(-1.5, 1.5)
fig.show()
I've seen solutions including legend.legendHandles[0]._size or various assortments of that, and it doesn't seem to change the size regardless of the value I set

Answer 1

The legend markers for the circles are different in size because the first circle has no edgecolor, while the two other ones have an edgecolor set via color. You may instead set the facecolor of the circle. Alternatively, you can set the linewidth of all 3 circles equal.
The legend marker for the line is so huge because it simply copies the attribute from the line in the plot. If you want to use a different linewidth, you can update it via the respective legend handler.
import matplotlib.pyplot as plt
from matplotlib.legend_handler import HandlerLine2D
def update_prop(handle, orig):
handle.update_from(orig)
handle.set_linewidth(2)
fig, ax = plt.subplots(figsize=(6.4, 6), dpi=200, frameon=False)
# 3 Circles, set the facecolor instead of edge- and face-color
ax.add_patch(plt.Circle((0,0), radius=1, alpha=0.9, zorder=0, label="Circle"))
ax.add_patch(plt.Circle((-1,0), radius=0.05, facecolor="y", label="Point on Circle"))
ax.add_patch(plt.Circle((1, 0), radius=0.05, facecolor="k", label="Opposite Point on Circle"))
# Line, update the linewidth via
ax.axvline(0, ymin=0.5-0.313, ymax=0.5+0.313, linewidth=12, zorder=1, c="g", label="Vertical Line")
ax.legend(loc=2, handler_map={plt.Line2D:HandlerLine2D(update_func=update_prop)})
ax.set_xlim(-2,1.2)
ax.set_ylim(-1.5, 1.5)
plt.show()