matplotlib
Variable names should generally be lowercase
In many places we have uppercase variables, e.g.
X = np.linspace(0, 2 * np.pi, 100)
Y = np.sin(X)
and likewise then in the plot functions.
This is against PEP-8 naming conventions and IMHO sets a bad example. At least 1D arrays should be lowercase. One may debate on 2D arrays, which have a history of using uppercase letters in the Matplotlib docs.
I use capital letters to indicate the variable is an array and I find this to be quite convenient. Since PEP-8 is a generic semantic-blind recommendation and I would prefer not to enforce it too strictly.
I use capital letters to indicate the variable is an array
Numpy and matplotlib docs generally don't do this. Changing naming conventions (whether better or not) may be confusing.
I think PEP-8 is confusing in that specific case. But ok to change names if really necessary.