How can I create a scatter plot legend without two symbols showing up each time? I can understand why you'd want this when you're joining symbols by lines, but for a pure scatter plot, all I want in the legend is one example of the symbol. This plot from a previous stackoverflow post shows the kind of thing I mean:
In the legend command you can use the scatterpoints option:
ax.legend(loc=0, scatterpoints = 1)
For a normal plot, it is the option numpoints.
Here you can find more information about the keyword arguments for the legend: http://matplotlib.sourceforge.net/api/pyplot_api.html#matplotlib.pyplot.legend
来源：https://stackoverflow.com/questions/6099799/how-to-create-a-scatter-plot-legend-with-only-one-symbol-for-each-label