Why do many examples use `fig, ax = plt.subplots()` in Matplotlib/pyplot/python

neelshiv picture neelshiv · Dec 8, 2015 · Viewed 211.1k times · Source

I'm learning to use matplotlib by studying examples, and a lot of examples seem to include a line like the following before creating a single plot...

fig, ax = plt.subplots()

Here are some examples...

I see this function used a lot, even though the example is only attempting to create a single chart. Is there some other advantage? The official demo for subplots() also uses f, ax = subplots when creating a single chart, and it only ever references ax after that. This is the code they use.

# Just a figure and one subplot
f, ax = plt.subplots()
ax.plot(x, y)
ax.set_title('Simple plot')

Answer

jonchar picture jonchar · Dec 8, 2015

plt.subplots() is a function that returns a tuple containing a figure and axes object(s). Thus when using fig, ax = plt.subplots() you unpack this tuple into the variables fig and ax. Having fig is useful if you want to change figure-level attributes or save the figure as an image file later (e.g. with fig.savefig('yourfilename.png')). You certainly don't have to use the returned figure object but many people do use it later so it's common to see. Also, all axes objects (the objects that have plotting methods), have a parent figure object anyway, thus:

fig, ax = plt.subplots()

is more concise than this:

fig = plt.figure()
ax = fig.add_subplot(111)