Can’t print a 10 from .format() in superscript in tex in matplotlib

Try replacing the line

    ax.set_title("$x^{}$".format(i+1))

with

    ax.set_title("$x^{{{}}}$".format(i+1))

Matplotlib supports the use of (some) LaTeX expressions in axis titles. In LaTeX, the ^ character causes the next character, or group, to be formatted in superscript. When processing x^10, LaTeX will only set the 1 in superscript, leaving the 0 on the same line as the x, but when processing x^{10} it will set 10 in superscript because 10 is inside the group that the braces { and } surround. (If it didn’t do this, how would it know when the superscript ended?)

When .format encounters {{ and }}, it takes them to mean that you want an actual { or } character in the resulting string, and that they are not part of a placeholder it has to fill with a value. The {} in the middle of "$x^{{{}}}$" is interpreted as the placeholder.

You end up with three pairs of braces, because it happens that { and } characters have a meaning to both the .format method and to LaTeX.