Symptom

Global Arguments now stop working in Python 3.9.8:

> az cloud show --query profile
{
  "endpoints": {
    "activeDirectory": "https://login.microsoftonline.com",
    ...

Notice --query doesn't take effact.

Root cause

This is due to the argparse breaking change python/cpython#28420 which aims to solve https://bugs.python.org/issue45235. Python 3.9.8 is the first released version with this change. It will spread to all Python versions later.

In Knack, global arguments are registered on all root/intermediate/leaf parsers, and they share the same dest. Previously, leaf-level arguments takes precedence. After this change, root-level arguments take precedence.

We are not sure if this is intended or not, as according to Semantic Versioning, a PATCH version update shouldn't cause breaking change.

Since Azure CLI does some trimming on the command table, using --query on the root parser won't work. We have to use Knack directly to demonstrate it:

Proposed solution

Knack should only register global arguments on leaf parsers to avoid this issue. We don't allow using global arguments in the middle of a command anyway:

• ✔ az cloud show --query profile
• ❌ az --query profile cloud show
• ❌ az cloud --query profile show

References

This issue is also affecting other CLI tools utilizing argparse:

• argparse subparser defaults in Python 3.9+ sopel-irc/sopel#2210

A related topic for --output was extensively discussed before:

• Specifying --output at top level corrupts subcommand configuration #7877