How do I autofit a figure size in matplotlib?

I tried to plot a figure to show all possible markers and got this undesired figure with plt.savefig,

This is caused by the small figure size (the default figure size: 800x600 pixels).

I can manually increase the figure size with fig.set_size_inches(w, h), but I don't know the exact size it should be. Is there a way to autofit the figure size?

I learnt from Resize a figure automatically in matplotlib that passing the option bbox_inches='tight' to plt.savefig can automatically resize a figure, but it doesn't work for me. I also tried plt.tight_layout(), it doesn't work either.

---

Here is the source code.

from __future__ import division

import matplotlib.pyplot as plt
import matplotlib
import math
import operator

def chunks(l, n):
    """Yield successive n-sized chunks from l."""
    for i in range(0, len(l), n):
        yield l[i:i+n]

def plot_all_marks(out_file):
    """plot all possible markers"""
    fig, axarr = plt.subplots(2, 2)
    fig.suptitle('All possible markers in Matplotlib')          # Add a centered title to the figure

    markers = matplotlib.lines.Line2D.markers   # all possiable markers, 35
    group_size = int(math.ceil(len(markers)/4))
    list_marker_s = sorted(markers.items(), key=operator.itemgetter(1)) # sorted by description

    for idx_chunk, l in enumerate(chunks(list_marker_s, group_size)):
        # for each group
        i, j = divmod(idx_chunk, 2)
        for idx, (marker, s) in enumerate(l):
            y = [-idx]*5
            axarr[i, j].plot(y, 'o',    marker=marker, 
                                        markeredgecolor='k',        # mec 
                                        markerfacecolor='b',        # mfc 
                                        markerfacecoloralt='r',     # mfcalt, set the alternate marker face color
                                        markeredgewidth=1.0,        # mew, float value in points
                                        fillstyle='none',           # fillstyles = ('full', 'left', 'right', 'bottom', 'top', 'none') 
                                        markevery=None,             # [None | int | length-2 tuple of int | slice | list/array of int | float | length-2 tuple of float]
                                        markersize=8, label=s)

            axarr[i, j].set_axis_off()
            axarr[i, j].legend(loc='center left')
            axarr[i, j].set_xlim(-4, 5)
            axarr[i, j].set_ylim(-group_size, 1)
            axarr[i, j].legend(loc='center left')

    plt.tight_layout()
    plt.savefig(out_file, bbox_inches='tight')

def main():
    # plot all markers
    out_file = 'all_marks.png'
    plot_all_marks(out_file)


if __name__ == '__main__':
    main()