Previous matplotlib had a bug. As per documentation, specifying empty

bmistree · tacaswell · commit 25f934e4ca00 · 2014-09-29T21:13:10.000-04:00
string for sym argument should prevent drawing fliers for boxplots.

As an example, the following script displays fliers in the boxplot
when it shouldn't.

    import matplotlib.pyplot as plt

    data = list(range(0,100)) + [200,-200,250,-250]
    bp = plt.boxplot(data,sym='',widths=.3)
    plt.show()

Added logic to ensure empty sym string does not display fliers.
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -3081,6 +3081,10 @@ def boxplot(self, x, notch=False, sym=None, vert=True, whis=1.5,
                     flierprops['markeredgecolor'] = color
                     flierprops['markerfacecolor'] = color
 
+        # do not show fliers if sym is empty string
+        if sym == '':
+            showfliers = False
+
         # replace medians if necessary:
         if usermedians is not None:
             if (len(np.ravel(usermedians)) != len(bxpstats) or
