Can I get some help plotting an IIR filter frequency response in Python?
We can't replace the learning experience of doing the actual homework, and coding questions should be posted on Stack Overflow, so below is not a complete solution but some hints in case this part wasn't clear: 

The frequency response is the magnitude and phase of the complex result for $H(z)$ when you use $z = e^{j\Omega}$, where $\Omega$ represents normalized radian frequency (normalized as it is the radian frequency divided by the sampling rate). This is the unit circle on the z-plane. 

That said, given the transfer function 

$$H(z) = \frac{0.125}{1-0.875z^{-1}}$$

To get the frequency response simply $z$ with $e^{j\Omega}$ and solve for the magnitude and phase as you sweep $\Omega$ over the frequencies of interest (such as from $0$ to $\pi$ as given in the linked problem, which is the equivalent of sweeping from DC to half the sampling rate.

These links may help if the above is confusing:

$e^{j\omega}$ on unit circle

How/why are the $\mathcal Z$-transform and unit delays related?