How to install ruamel.yaml on a buildroot environment - ruamel.yaml

Question

ruamel.yaml seems to require PIP to install, which is not the default buildroot solution to build and install a Python package.
Is is possible to -at least- install a pure Python version of ruamel.yaml into a buildroot image - and how to circumvent the pip limitation?
Is is possible to cross-build ruamel.yaml?
Forcing RUAMEL_NO_PIP_INSTALL_CHECK env. var. does not help:
test compiling test_ruamel_yaml
running install
Checking .pth file support in ...
Failed to import the site module
ModuleNotFoundError: No module named '_sysconfigdata_m_linux_arm-linux-gnueabihf'
error: command '.../output/host/bin/python' failed with exit status 1
package/pkg-generic.mk:310: recipe for target '.../output/build/python-ruamel-yaml-0.15.45/.stamp_target_installed' failed

Answer 1

ruamel.yaml indeed requires pip to install from PyPI (using the .tar.gz or a .whl appropriate for your platform), this is documented.
The reason for this is that the fixes necessary to enable nested package installs where only implemented for pip (and not for easy_install or python setup.py installs).
That however does not preclude you from using ruamel.yaml, especially if you don't need the C extension (which is checked for at load time).
You can either check out a tagged version from bitbucket or untar a .tar.gz from PyPI and move the result to your site-packages directory:
$ virtualenv /tmp/ruamel_yaml_no_pip
Using base prefix '/opt/python/3.7'
New python executable in /tmp/ruamel_yaml_no_pip/bin/python
Installing setuptools, pip, wheel...done.
$ cd /tmp/ruamel_yaml_no_pip/
$ source bin/activate
(ruamel_yaml_no_pip) $ mkdir lib/python3.7/site-packages/ruamel/
(ruamel_yaml_no_pip) $ touch lib/python3.7/site-packages/ruamel/__init__.py
(ruamel_yaml_no_pip) $ wget -q https://files.pythonhosted.org/packages/63/a5/dba37230d6cf51f4cc19a486faf0f06871d9e87d25df0171b3225d20fc68/ruamel.yaml-0.15.45.tar.gz
(ruamel_yaml_no_pip) $ python -m ruamel.yaml
/tmp/ruamel_yaml_no_pip/bin/python: Error while finding module specification for 'ruamel.yaml' (ModuleNotFoundError: No module named 'ruamel')
(ruamel_yaml_no_pip) $ tar xf ruamel.yaml-0.15.45.tar.gz
(ruamel_yaml_no_pip) $ mv ruamel.yaml-0.15.45 lib/python3.7/site-packages/ruamel/yaml
(ruamel_yaml_no_pip) $ python -c 'from ruamel.yaml import YAML; print(YAML().load("{hello: world}")["hello"])'
world
(ruamel_yaml_no_pip)
(ruamel_yaml_no_pip) $ python -c 'from ruamel.yaml import __with_libyaml__ as X; print(X)'
False
(The URL is copied from the 0.15.45 project download page)
For development I normally just make a soft link from a virtualenv's site-packages to my ruamel directory.
I don't know how and if that translates to a buildroot environment (if so please publish your result).

Answer 2

I overlooked the buildroot documentation.
There is a critical parameter to define: SETUP_TYPE = setuptools rather than SETUP_TYPE = distutils.
With the following snippet:
PYTHON_RUAMEL_YAML_VERSION = 0.15.45
PYTHON_RUAMEL_YAML_SOURCE = ruamel.yaml-$(PYTHON_RUAMEL_YAML_VERSION).tar.gz
PYTHON_RUAMEL_YAML_SITE = https://pypi.python.org/packages/63/a5/dba37230d6cf51f4cc19a486faf0f06871d9e87d25df0171b3225d20fc68
PYTHON_RUAMEL_YAML_SETUP_TYPE = setuptools
PYTHON_RUAMEL_YAML_LICENSE = MIT
PYTHON_RUAMEL_YAML_LICENSE_FILES = LICENSE
PYTHON_RUAMEL_YAML_ENV += RUAMEL_NO_PIP_INSTALL_CHECK=1
$(eval $(python-package))
ruamel.yaml installs perfectly on the target image.