Error following f0cal/core Quick Start workflow after f0cal/bootstrap

Reproduce the Quick Start workflow with the commands in the issue, then inspect the downloaded conanfile.py around requirements() line 145 and the pip_install traceback at line 20. Confirm the cause of the TypeError and verify that the same workflow completes without the reported error.

Immediately after following the Quick Start workflow in f0cal/bootstrap, while following the Quick Start instructions in f0cal/core, I receive an error with pip_install(req) 'TypeError: 'module' object is not callable'.

Steps:

curl bootstrap.f0cal.com/master | python3 - -v f0cal/venv git
cd f0cal
source venv/bin/activate
eval $(f0cal env activate -a)
conan install f0cal-opencv/4.0.1@f0cal/testing --build=missing

Output from last step (with error):

conan install f0cal-opencv/4.0.1@f0cal/testing --build=missing
Configuration:
[settings]
arch=x86_64
arch_build=x86_64
build_type=Release
compiler=gcc
compiler.libcxx=libstdc++11
compiler.version=7
os=Linux
os_build=Linux
[options]
[build_requires]
[env]

f0cal-opencv/4.0.1@f0cal/testing: Not found in local cache, looking in remotes...
f0cal-opencv/4.0.1@f0cal/testing: Trying with 'conan-center'...
f0cal-opencv/4.0.1@f0cal/testing: Trying with 'f0cal'...
Downloading conanmanifest.txt: 100%|##########| 121/121 [00:00<00:00, 105kB/s]
Downloading conanfile.py: 100%|##########| 2.00k/2.00k [00:00<00:00, 2.30MB/s]
f0cal-opencv/4.0.1@f0cal/testing: Downloaded recipe revision 0
opencv/4.0.1@f0cal/testing: Not found in local cache, looking in remotes...
opencv/4.0.1@f0cal/testing: Trying with 'conan-center'...
opencv/4.0.1@f0cal/testing: Trying with 'f0cal'...
Downloading conanmanifest.txt: 100%|##########| 121/121 [00:00<00:00, 120kB/s]
Downloading conanfile.py: 100%|##########| 17.3k/17.3k [00:01<00:00, 15.2kB/s]
opencv/4.0.1@f0cal/testing: Downloaded recipe revision 0
ERROR: opencv/4.0.1@f0cal/testing: Error in requirements() method, line 145
	pip_install(req)
while calling 'pip_install', line 20
	pipmain(['install', package])
	TypeError: 'module' object is not callable