I was trying to install VPython. The first message records a Debian package whose dependencies targeted Python 2.5. A follow-up records the actual experiment: I changed the upper Python constraint from less than 2.6 to less than 2.7, installed the package, and got segfaults under Python 2.6 while it ran under 2.5. The metadata edit opened the gate. It did not make the artifact work in the new runtime.
VPython reached its compiled C++ core through Boost.Python. Relaxing the installer constraint left those components unchanged. The next useful experiment was to rebuild them against Python 2.6 and compare that build with the original package.
A dependency bound can describe a tested support range or a binary requirement. The package manager enforces the declaration; testing the compiled artifact establishes whether it works with the chosen interpreter.