upd

examples/simple_plot.py

@@ -2,45 +2,46 @@
 #
 #   a simple matplotlib plot - testing for pipelines
 #
-#   parent shell can optionally do:
-#       export MPLBACKEND=agg
+#   setting the backend:
+#     1.  rcParams["backend"] parameter in your matplotlibrc file
+#     2.  The MPLBACKEND environment variable
+#     3.  The function matplotlib.use()
 #
 _version = "3-sep-2023"
-_mode = 0
 
 import os
 import sys
-
 import numpy as np
 
-if __name__ == "__main__":
-    if len(sys.argv) > 1:
-        _mode = int(sys.argv[1])
-        plotfile = 'simple_plot.png'
-    else:
-        _mode = 0
-        plotfile = None
+if len(sys.argv) > 1:
+    _mode = int(sys.argv[1])
+    plotfile = 'simple_plot.png'
+else:
+    _mode = 0
+    plotfile = None
 
-    import matplotlib
+import matplotlib
+if 'MPLBACKEND' in os.environ:
+    print('$MPLBACKEND :',os.environ['MPLBACKEND'])
+    matplotlib.use(os.environ['MPLBACKEND'])          # isn't this redundant?
+else:
+    print("no $MPLBACKEND used")
     if _mode == 0:
         matplotlib.use('qt5agg')
     else:
         matplotlib.use('agg')
-    import matplotlib.pyplot as plt
-    if 'MPLBACKEND' in os.environ:
-        print('$MPLBACKEND :',os.environ['MPLBACKEND'])
-    else:
-        print("no $MPLBACKEND used")
-    print('mpl backend :',matplotlib.get_backend())
 
-    x = np.arange(0,2,0.1)
-    y = np.sqrt(x)
+import matplotlib.pyplot as plt
+print('mpl backend :',matplotlib.get_backend())
+
+x = np.arange(0,2,0.1)
+y = np.sqrt(x)
 
-    plt.figure()
-    plt.plot(x,y, label="test");
-    plt.legend()
-    if plotfile == None:
-        plt.show()
-    else:
-        plt.savefig(plotfile)
-        print("Wrote",plotfile)
+plt.figure()
+plt.plot(x,y, label="test");
+plt.legend()
+if plotfile == None:
+    plt.show()
+else:
+    plt.savefig(plotfile)
+    print("Wrote",plotfile)