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--- other:python:matplotlib_by_jyp [2020/03/31 12:49] – [Misc Matplotlib tricks] Improved jypeter
+++ other:python:matplotlib_by_jyp [2020/03/31 16:26] – [Starting (and more) with matplotlib] Improved offline plot creation jypeter
@@ Line 104: / Line 104: @@
     - you can use **transparency** to partially show what is behind some markers or other objects. Many //artists// accept the ''alpha'' parameter where ''0.0'' means that the object is completely transparent, and ''1.0'' means completely opaque\\ e.g. ''my_plot.scatter(..., alpha=0.7)''
     - sometimes the results of the python/matplolib commands are displayed immediately, sometimes not. It depends if you are in [[http://matplotlib.org/faq/usage_faq.html#what-is-interactive-mode|interactive or non-interactive]] mode
-    - if your matplotlib is executed in a batch script, it will generate an error when trying to create (''show()'') a plot, because matplotlib expects to be able to display the figure on a screen by default.
+    - if your matplotlib is executed in a batch script, it will generate an error when trying to create (''show()'') a plot, because matplotlib expects to be able to display the figure on a screen (with an X server running) by default.\\ Find out how to deal with this in [[other:python:matplotlib_by_jyp#creating_a_plot_offline|Creating a plot offline]].
-      * Check how you can [[https://matplotlib.org/faq/howto_faq.html?highlight=web#generate-images-without-having-a-window-appear|generate images offline]]
     - the documentation may mention [[http://matplotlib.org/faq/usage_faq.html#what-is-a-backend|backends]]. What?? Basically, you use python commands to create a plot, and the backend is the //thing// that will render your plot on the screen or in a file (png, pdf, etc...)
   - Read the [[https://github.com/rougier/matplotlib-tutorial|Matplotlib tutorial by Nicolas Rougier]]
@@ Line 186: / Line 185: @@
 ===== Misc Matplotlib tricks =====
+==== Creating a plot offline ====
+You may need to create a plot offline when your network connection is not good enough, you don't have an X server running to display the plot (possibly because the script is running on a cluster), etc... This is easily done with the following code:
+<code># offline_plot = False
+offline_plot = True
+import matplotlib as mpl
+if offline_plot:
+    # Define the graphic back-end BEFORE importing pyplot
+    mpl.use('Agg')
+# Import the rest of the matplotlib based modules
+import matplotlib.pyplot as plt
+[ ...your actual code... ]
+# Done at last! Save the result
+my_page.savefig(out_name, dpi=300, transparent=True, bbox_inches='tight')
+if not offline_plot:
+    # Enter the interactive mode to display the plot
+    plt.show()</code>
+Note: see also [[https://matplotlib.org/gallery/user_interfaces/canvasagg.html|CanvasAgg demo]] for a pure offline plot, and [[https://matplotlib.org/faq/howto_faq.html?highlight=web#howto-webapp|How to use Matplotlib in a web application server]]. But the code above is much easier!
 ==== Specifying the background color of a plot ====