other:python:matplotlib_by_jyp
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other:python:matplotlib_by_jyp [2020/03/31 10:49] jypeter [Misc Matplotlib tricks] Improved |
other:python:matplotlib_by_jyp [2020/03/31 14:26] jypeter [Starting (and more) with matplotlib] Improved offline plot creation |
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| - 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)'' | - 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 | - 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...) | - 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]] | - Read the [[https://github.com/rougier/matplotlib-tutorial|Matplotlib tutorial by Nicolas Rougier]] | ||
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| ===== Misc Matplotlib tricks ===== | ===== 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 ==== | ==== Specifying the background color of a plot ==== | ||
other/python/matplotlib_by_jyp.txt · Last modified: 2023/10/26 08:39 by jypeter
