When using FormatStrFormatter on the x-axis, the negative numbers have a dash - in front instead of a minus −.

θ = linspace(-1.5, 0) * 2 * π
y = sin(θ)
plot(θ / π, y)
gca().xaxis.set_major_formatter(FormatStrFormatter('%g π'))

Without the formatter, all looks good.

x = linspace(-1.5, 0)
y = sin(x * 2 * π)
plot(x, y)

I'm wondering who's handling the conversion of the dash into a minus, and how to recreate that when using FormatStrFormatter.