What wizardry is being used to display Matplotlib color maps in an ipython console? - matplotlib

Question

I am working with Matplotlib color maps, and I also happen to be working with the Spyder IDE, which has an ipython console.
As you can see from the screen shot, the ipython console showed me a graphical representation of the color map object. This was unexpected and very helpful.
Normally I expect to see a string representation of an object, as you might see from the print() function call. Function calls to print() and repr() are shown, and they produce text, as is more typical.
I would like my own code to output this graphical representation when it is generating output. I have been poking through the matplotlib.colors.Colormap internals, and so far I haven't been able to figure out how. What is ipython doing? How can I do the same?
Thanks!

Answer 1

This rather seems like a ipython/jupyter feature. ipython detects the object and produces automatically a plot to preview the colormap.
Here using jupyter:

Answer 2

IPython looks if an object has a _repr_html_; if so, it calls it and displays the output as HTML. Here's an example (I ran this in Jupyter but it works the same as long as you're running IPython):
class MyCoolObject:
def _repr_html_(self):
return ("<h1>hello!</h1> <p>this is some html </p>"
"I can even put images:"
"<img src='https://upload.wikimedia.org/wikipedia"
"/commons/thumb/3/38/Jupyter_logo.svg"
"/44px-Jupyter_logo.svg.png'></img>")
MyCoolObject()

Answer 3

To add on to Eduardo's answer, from everything I've read adding a _repr_html_ method should make iPython display the object when you type it into the console. I also use spyder though, and could not get it to work the way I expected. This simple wrapper class should allow you to display any html:
class displayedHTML:
def __init__(self, html):
self.html = html
def _repr_html_(self):
return self.html
But as you can see it does not work for me, instead showing the (implicitly defined) __repr__ of the class.
In [2]: obj = displayedHTML("<h1>" + "hello world" + "</h1>")
In [3]: obj
Out[3]: <__main__.displayedHTML at 0x1e8cda8f0d0>
I was not able to find the reason why this does not work, but I found a workaround if you just want to display a matplotlib colormap in the console from code (like I did).
Since know the matplotlib object works correctly, we can just give it to the ipython display function:
from IPython.display import display #Included without import since IPython 5.4 and 6.1
viridis = matplotlib.cm.get_cmap('viridis')
display(viridis)
And for me this works...
not_allowed_to_insert_pictures_yet.jpg
Hope this helps!