Using matplotlib scatter markers in text of legend together with Latex

Question

I have a plot with an inset. The latter has a legend, in whose text I would like to use matplotlib scatter markers. I also want to be able to use LaTeX at the same time for all the labels and legends. The reason I am mentioning this is because I had a look at this thread and the solutions there don't work for me. I will explain why bellow.

Here is an example code (sorry for the functions I am plotting, couldn't think of anything)

# -*- coding: utf-8 -*-
import numpy as np
import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid.inset_locator import (inset_axes, InsetPosition, mark_inset)
from matplotlib import rc
rc('text', usetex=True)

N = 50
x = np.random.rand(N)
y = np.random.rand(N)

fig, ax1 = plt.subplots()

ax1.scatter(x, np.cos(x), color = 'blue', marker = "D", s=47.5, label = r'$\cos$')
ax1.scatter(y, np.sin(y), color = 'cyan', marker = "*", alpha = 0.85, label = r'$\sin$')
ax1box = ax1.get_position()
x_value = -0.13
y_value = 0.675
legend=ax1.legend(loc = (ax1box.x0 + x_value, ax1box.y0 + y_value), handletextpad=0.1, prop={'size':8})
frame = legend.get_frame()
frame.set_alpha(0)
frame.set_linewidth(0)

ax2 = plt.axes([0.5,0.5,0.5,0.5])
ip = InsetPosition(ax1, [0.55,0,0.45,0.40])
ax2.set_axes_locator(ip)
ax2.scatter(x, np.tan(x), color = 'gray', marker = "v", s=15, label = r'Insert blue square marker here')
ax2.scatter(y, np.log(y)+1, color = 'brown', marker = "4", s=15, label = r'Insert cyan star marker here')
ax2.xaxis.tick_top()
ax2.xaxis.set_label_position('top')
ax2.yaxis.tick_right()
legend2=ax2.legend(loc = 'lower right', handletextpad=0.1, prop={'size':7})
frame2 = legend2.get_frame()
frame2.set_alpha(0)
frame2.set_linewidth(0)

plt.show()

If I am to go with the advice in here about LaTeX and try with

ax2.scatter(x, np.tan(x), color = 'gray', marker = "v", s=15, label = r'$\square$')

the plot shows with no legend in the inset.

If, instead, I decide to implement the unicode solution

ax2.scatter(x, np.tan(x), color = 'gray', marker = "v", s=15, label = '●')

I get the following error

Exception in Tkinter callback
Traceback (most recent call last):
  File "/usr/lib/python3.5/tkinter/__init__.py", line 1562, in __call__
    return self.func(*args)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/backends/backend_tkagg.py", line 280, in resize
    self.show()
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/backends/backend_tkagg.py", line 351, in draw
    FigureCanvasAgg.draw(self)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/backends/backend_agg.py", line 464, in draw
    self.figure.draw(self.renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/artist.py", line 63, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/figure.py", line 1144, in draw
    renderer, self, dsu, self.suppressComposite)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/image.py", line 139, in _draw_list_compositing_images
    a.draw(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/artist.py", line 63, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/axes/_base.py", line 2426, in draw
    mimage._draw_list_compositing_images(renderer, self, dsu)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/image.py", line 139, in _draw_list_compositing_images
    a.draw(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/artist.py", line 63, in draw_wrapper
    draw(artist, renderer, *args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/legend.py", line 471, in draw
    bbox = self._legend_box.get_window_extent(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 269, in get_window_extent
    w, h, xd, yd, offsets = self.get_extent_offsets(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 391, in get_extent_offsets
    for c in self.get_visible_children()]
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 391, in <listcomp>
    for c in self.get_visible_children()]
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 262, in get_extent
    w, h, xd, yd, offsets = self.get_extent_offsets(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 462, in get_extent_offsets
    for c in self.get_visible_children()]
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 462, in <listcomp>
    for c in self.get_visible_children()]
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 262, in get_extent
    w, h, xd, yd, offsets = self.get_extent_offsets(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 391, in get_extent_offsets
    for c in self.get_visible_children()]
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 391, in <listcomp>
    for c in self.get_visible_children()]
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 262, in get_extent
    w, h, xd, yd, offsets = self.get_extent_offsets(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 462, in get_extent_offsets
    for c in self.get_visible_children()]
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 462, in <listcomp>
    for c in self.get_visible_children()]
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/offsetbox.py", line 835, in get_extent
    bbox, info, d = self._text._get_layout(renderer)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/text.py", line 362, in _get_layout
    ismath=ismath)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/backends/backend_agg.py", line 230, in get_text_width_height_descent
    renderer=self)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/texmanager.py", line 676, in get_text_width_height_descent
    dvifile = self.make_dvi(tex, fontsize)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/texmanager.py", line 399, in make_dvi
    texfile = self.make_tex(tex, fontsize)
  File "/usr/local/lib/python3.5/dist-packages/matplotlib/texmanager.py", line 314, in make_tex
    fh.write(s.encode('ascii'))
UnicodeEncodeError: 'ascii' codec can't encode character '\u25cf' in position 226: ordinal not in range(128) 

Which seems to come from the fact that I am using LaTeX, as If I comment out

# from matplotlib import rc
# rc('text', usetex=True)

Then I get everything working, but without LaTeX. (Well the circle I get is black, I haven't looked into whether it is possible to change its colour yet). I do want LaTeX, though, so this is not good for me.

Answer 1

As The Great, Big List of LaTeX Symbols tells us, \square is an AMS symbol. So, in order to use it you have to put \usepackage{amssymb} in your preamble, which can be done with

rc('text', usetex=True)
rc('text.latex', preamble=r'\usepackage{amssymb}')