Specifying dictionary argument with dict() or braces matters in set_bbox #1934

lguez opened this Issue Apr 22, 2013 · 6 comments

4 participants


In matplotlib home page, there is a link to a tutorial by Nicolas Rougier. In the section of the tutorial entitled "Devil is in the details", the script:


produces the figure displayed on the web page. Line 48 of the script is:

label.set_bbox(dict(facecolor='white', edgecolor='None', alpha=0.65 ))

If we replace this line by:

label.set_bbox({"facecolor": "white", "edgecolor": "None","alpha":0.65})

then the edgecolor request is not taken into account. The two statements above should be equivalent. The author of the tutorial, Nicolas Rougier, is surprised too. People on stackoverflow think it is a matplotlib bug:


Matplotlib Developers member

The problem is not with the way you instantiate a dictionary but the order. If I run the test program, sometimes I see the edge and sometimes not depending on the random ordering of the dictionary.

The issue arrises when alpha comes after edgecolor and the fact that there is no special edgecolor for "none". Instead when one sets edgecolor to "none" it gets transfered to a RGBA tuple of (0,0,0,0). Then when alpha is set it makes it (0,0,0,0.65) in the example (i.e. black with an alpha of 0.65) which is why the edge shows up.

I believe the solution is to actually allow colors of None but code would have to change to accept and interpret a None value in addition to the RGBA tuple, i.e. a color of none and black with zero alpha are indeed different.

Matplotlib Developers member

@cimarronm - is this now fixed?


Thank you. Am I supposed to close this issue myself? (I do not have the update with the correction myself.)


@pelson: I tested it and it is fixed thanks to the good work from @Westacular

Matplotlib Developers member

Great. thanks for the update.

@pelson pelson closed this May 15, 2013
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