Clean two scaled y-axis demo.

matplotlib · gabraganca · Jun 29, 2013 · Jun 29, 2013 · Jun 29, 2013 · Jun 29, 2013
commit fcc48f59aca2eeea9351d019c7fae5e45fd74693
diff --git a/examples/api/fahrenheit_celsius_scales.py b/examples/api/fahrenheit_celsius_scales.py
diff --git a/examples/subplots_axes_and_figures/fahrenheit_celsius_scales.py b/examples/subplots_axes_and_figures/fahrenheit_celsius_scales.py
@@ -0,0 +1,35 @@
+"""
+Demo of how to display two scales on the left and right y axis.
+
+This example uses the Fahrenheit and Celsius scales.
+"""
+import matplotlib.pyplot as plt
+import numpy as np
+
+fig, ax1 = plt.subplots()  # ax1 is the Fahrenheit scale
+ax2 = ax1.twinx()          # ax2 is the Celsius scale
+
+def fahrenheit2celsius(temp):
+    """
+    Returns temperature in Celsius.
+    """
+    return (5./9.)*(temp - 32)
+
+def convert_ax2_to_celsius(ax1):
+    """
+    Update second axis according with first axis.
+    """
+    y1, y2 = ax1.get_ylim()
+    ax2.set_ylim(fahrenheit2celsius(y1), fahrenheit2celsius(y2))
+    ax2.figure.canvas.draw()
+
+# automatically update ylim of ax2 when ylim of ax1 changes.
+ax1.callbacks.connect("ylim_changed", convert_ax2_to_celsius)
+ax1.plot(np.linspace(-40, 120, 100))
+ax1.set_xlim(0, 100)
+
+ax1.set_title('Two scales: Fahrenheit and Celsius')
+ax1.set_ylabel('Fahrenheit')
+ax2.set_ylabel('Celsius')
+
+plt.show()