and print(default_flags) on my local machine just before with subtest("Create the NixOS configuration"): gives:

{'hdaInterface': 'virtio', 'hda': 'vm-state-machine/machine.qcow2', 'qemuFlags': '-cpu max -m 1024'}

It looks like python would be configured to reset the locals() dict within the scope of a function:

{'hdaInterface': 'virtio', 'hda': 'vm-state-machine/machine.qcow2', 'qemuFlags': '-cpu max -m 1024'}
# within create_machine_named(name):
===locals===: {'name': 'boot-after-install'}

Solution:

• exec(x) -- globals initialized at the moment exec function is initialized
• exec(x, globals()) -- globals initialized at the moment the function is called
• default_flags was a global symbol

Solution:

• exec(x) -- globals initialized at the moment exec function object is initialized
• exec(x, globals()) -- globals initialized at the moment the function object is called
• default_flags was a global symbol

Solution:

• exec(x) -- globals initialized at the moment exec function object is initialized
• exec(x, globals()) -- globals initialized at the moment the function object is called
• default_flags was a global symbol