Problem

I mistakenly supplied"blue\n" as the argumentc formatplotlib.axes.Axes.scatter, thenmatplitlib claimed for illegal color name like this:

ValueError: 'c' argument must be a color, a sequence of colors, or a sequence of numbers, not blue

I was not aware that the argument actually contained a trailing newline so I was very confused.

Proposed solution

The error message would be nicer if it outputs user's input viarepr.
For example, in this case the error messagehere can be easily replced with:

raiseValueError(f"'c' argument must be a color, a sequence of colors, "f"or a sequence of numbers, not{c!r}")from

so that we may now get an easy-to-troubleshoot error like this:

ValueError: 'c' argument must be a color, a sequence of colors, or a sequence of numbers, not "blue\n"

This kind of improvement can be applied to many other places.