未知的Matplotlib错误

Question

我收到以下错误，但我无法确定应该修复的内容：

python-2.7.4_scipy0.13/lib/python2.7/site-packages/matplotlib/axes.py:2757: UserWarning: Attempting to set identical bottom==top results
in singular transformations; automatically expanding.
bottom=0, top=0.0
  + 'bottom=%s, top=%s') % (bottom, top))

代码是：

plt.scatter(chart_dict[chart][0], chart_dict[chart][1], c=colours[count], alpha=1.0, label=chart, lw = 0)
plt.tight_layout()
plt.ylabel(titles_markers[2])
plt.xlabel(titles_markers[1])
plt.yscale('log')
plt.grid(b=True, which='major', color='b', linestyle='-')
plt.title(titles_markers[0])
plt.legend()
plt.savefig(os.path.join(directory, titles_markers[0].replace(' ', '_')+'.png'))