matplotlib: Set width or height of figure without changing aspect ratio

Question

I'd like to choose the width of a figure, while still letting matplotlib choose the aspect ratio that it finds suitable. Every method I know to change the figure size requires a (width, height) tuple, which forces a certain aspect ratio. Is there any way to specify just the width (or just the height) and allow matplotlib to choose a suitable aspect ratio?

Answer 1

From what I understand, matplotlib does not "choose" a suitable aspect ratio per se. Instead, axes automatically fill to the size of the figure. Thus by setting the figure size with a (width, height) tuple you are also setting it's aspect ratio (taking into account the number of subplot axes within the figure as well). Perhaps the axes method set_aspect will help you? It lets you explicitly set the aspect ratio for an axes object within a figure.

For example, the following will produce a 4"x2" figure but the axes within it will have a 1:1 aspect ratio:

  fig, ax = plt.subplots(figsize=(4,2))
  ax.set_aspect('equal')

The method set_aspect can also take a height:width number instead. You could use this to force the axes within to keep a specific aspect ratio regardless of the figure dimensions you choose.

EDIT: This post may also be helpful.

Answer 2

I've learned that matplotlib actually just uses a constant default figure size for all figures. This value is stored in the rcParams, and can be viewed with

plt.rcParams["figure.figsize"]

This returns [6.0, 4.0] for me.

If you want to keep the same width to height ratio (ie "aspect ratio"), you can, for example, double it with:

plt.rcParams["figure.figsize"] = [2 * i for i in plt.rcParams["figure.figsize"]]