ensure integer value ticks

cammil · cammil · commit 7e44f353744e · 2015-09-14T16:16:55.000+01:00
diff --git a/examples/ticks_and_spines/tick_labels_from_values.py b/examples/ticks_and_spines/tick_labels_from_values.py
@@ -9,28 +9,34 @@
 In this case may be better to determine the tick label from the value
 at the tick. The following example shows how to do this.
 
-NB: You may want to combine the solution below with 
-`xaxis.set_major_locator(MaxNLocator(integer=True))` to ensure
-that tick values are always at integer values, and therefore always use
-the appropriate label.
+NB: The MaxNLocator is used here to ensure that the tick
+values take integer values. As such, we need to catch
+any IndexErrors in the format function where we have not
+defined a label for that particular tick
 
 """
 
 
 
 import matplotlib.pyplot as plt
-from matplotlib.ticker import FuncFormatter
+from matplotlib.ticker import FuncFormatter, MaxNLocator
+
 
 fig = plt.figure()
 ax = fig.add_subplot(111)
 xs = range(26)
 ys = range(26)
 labels = list('abcdefghijklmnopqrstuvwxyz')
 
-def format_fn(tick_val, tick_pos): 
-    return labels[int(tick_val)]
+def format_fn(tick_val, tick_pos):
+    try:
+        return labels[int(tick_val)]
+    except IndexError:
+        # no label for this tick
+        return ''
 
 ax.xaxis.set_major_formatter(FuncFormatter(format_fn))
+ax.xaxis.set_major_locator(MaxNLocator(integer=True))
 
 ax.plot(xs, ys)
 plt.show()
