pygal rendering png/svg black pictures

Question

I am using python (with a virtual env in LinuxMint), I installed pygal.

Everything works fine (rendering to html) but not rendering to svg or png . The result : Nothing but a black background.

I installed cssselect and tinycss like mentioned here .

It works for the first time, but when retrying, I had the same issue .

(I don't know if this is related or not, but this happens to me when exporting a photo using darktable last week)

I use the example from the website of pygal:

import pygal                                                       # First import pygal
bar_chart = pygal.Bar()                                            # Then create a bar graph object
bar_chart.add('Fibonacci', [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55])  # Add some values
bar_chart.render_to_file('bar_chart.svg')                          # Save the svg to a file

EDIT:

bar_chart.render_to_png('bar_chart.png')

is working now .

But not:

bar_chart.render_to_file('bar_chart.svg')

Answer 1

You need to install lxml as well. So assuming you are in a virtualenv run the following command on your bash/zsh prompt:

pip install lxml

If you only have the other 3 libraries, i.e. cssselect, pycairo, tinycss. Then you will be able to properly render an SVG but the PNG render function will produce a solid black image file (without lxml installed)

The gist below shows all the steps:

[FIRST: install the required libraries]

• pip install lxml
• pip install cairosvg
• pip install tinycss
• pip install cssselect

[SECOND: create the file]

"""
pygal_render_png
""""
import pygal

bar_chart = pygal.Bar()
bar_chart.add('Fibonacci', [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55])
bar_chart.render_to_file('bar_chart.svg')
bar_chart.render_to_png(filename='bar_chart.png')

If you get black svg images in Image Viewer (Ubuntu) or Gimp, try opening the image in Chrome.