Why is cython expressing different Python requirements in the same build? - conda-build

Question

In trying to build Chaco using the following conda command:
conda build --python=3.9 --numpy=1.23 --use-local -c dbanas -c defaults -c conda-forge conda.recipe/chaco/
and the following meta.yaml file:
{% set name = "chaco" %}
{% set version = "5.1.1" %}
{% set enable_version = "5.3.1" %}
package:
name: "{{ name|lower }}"
version: "{{ version }}"
source:
git_url: https://github.com/enthought/chaco.git
git_rev: {{ version }}
build:
number: 1
script: "{{ PYTHON }} -m pip install . --no-deps --ignore-installed -vv "
requirements:
build:
- cmake
- Cython
- enable ={{ enable_version }}
- git
- importlib_resources
- numpy x.x
- pyface >=7.4.2
- python
- setuptools
- vs2019_win-64 # Uncomment for Windows build only.
# - {{compiler('c')}} # Would like to get one of these working, instead of above hack.
# - {{compiler('cxx')}}
run:
- Cython
- enable ={{ enable_version }}
- importlib_resources
- numpy x.x
- pyface >=7.4.2
- python
test:
# Python imports
imports:
- chaco
- chaco.api
# - chaco.contour
# - chaco.downsample
# - chaco.downsample.tests
# - chaco.layers
# - chaco.overlays
# - chaco.plugin
# - chaco.scales
# - chaco.scales.tests
# - chaco.shell
# - chaco.tests
# - chaco.tools
# - chaco.tools.tests
# - chaco.tools.toolbars
- chaco.ui
# commands:
# You can put test commands to be run here. Use this to test that the
# entry points work.
# You can also put a file called run_test.py in the recipe that will be run
# at test time.
# requires:
# Put any additional test requirements here. For example
# - nose
about:
home: http://docs.enthought.com/chaco
license: BSD License
summary: 'interactive 2-dimensional plotting'
license_family: BSD
# See
# http://docs.continuum.io/conda/build.html for
# more information about meta.yaml
extra:
recipe-maintainers:
- capn-freako
I'm getting a dependency version conflict report, which includes the following two very different expectations of cython, regarding Python version:
{snip}
Package vc conflicts for:
{snip}
cython -> python[version='>=2.7,<2.8.0a0'] -> vc[version='10.*|>=9,<10.0a0']
{snip}
Package python conflicts for:
{snip}
cython -> python[version='2.7.*|3.5.*|3.6.*|>=2.7,<2.8.0a0|>=3.10,<3.11.0a0|>=3.7,<3.8.0a0|>=3.8,<3.9.0a0|>=3.9,<3.10.0a0|>=3.6,<3.7.0a0|>=3.5,<3.6.0a0|>=3.11,<3.12.0a0|3.4.*']
{snip}
Why is cython expressing such a narrow range of acceptable Python versions in the first case (none of which are 3.*!) and such a broad range in the second case?
I also see this strange message, at the very end of my output:
The following specifications were found to be incompatible with your system:
- feature:/win-64::__win==0=0
- feature:|#/win-64::__win==0=0
- setuptools -> wincertstore[version='>=0.2'] -> __win
Your installed version is: 0