Cannot package a PyPI tool

[lainiwa]

Hello!

I was playing around with Guix and I tried to package a termtosvg tool 
just for an exercise.

I have a
export GUIX_PACKAGE_PATH=~/guix-packages
setting and I create my *.scm files in that directory.

my-hello.scm from the documentation worked fine, however when I tried to 
package a more "real-world" example I got an error:

------------------------------
name: python-termtosvg
version: 1.1.0
outputs: out
Backtrace:
           1 (primitive-load "/home/lain/.config/guix/current/bin/gu…")
In guix/ui.scm:
  1824:12  0 (run-guix-command _ . _)

guix/ui.scm:1824:12: In procedure run-guix-command:
error: python-lxml: unbound variable
------------------------------

My python-termtosvg.scm content: https://pastebin.com/cenixFh7

Can I somehow make Guix see python-lxml from the main channel (or maybe 
solve the problem in some other way)?