There's the following script:

#! /usr/bin/python

import rpm

if __name__ == '__main__':
    spec = rpm.spec(__file__)

That outputs:

error: line 3: Unknown tag: import rpm

In the stdout.

If one creates an empty dir and points the rpm.spec call to it there's even more:
error: Name field must be present in package: (main package)
error: Version field must be present in package: (main package)
error: Release field must be present in package: (main package)
error: Summary field must be present in package: (main package)
error: License field must be present in package: (main package)

If the lib outputs these into stdout, the output of client programs like DNF can look overly dramatic and confusing.