3.6. Python 3 Migration

In UCS 5.0 all UCR templates and UCR modules must be compatible with Python 2 and Python 3. This must also be the case for UCS 4.4 and newer, because during the upgrade to UCS 5.0 UCR templates can be evaluated with either Python version.

Many templates simply use the Python 2 print statement:

print configRegistry.get('my/variable')

In Python 3 print() is a function, which requires parenthesis to be added:

print(configRegistry.get('my/variable'))

This way the statement is both compatible with Python 2 and Python 3. But it breaks if multiple arguments are supplied or extra arguments from the Python 3 syntax are used:

print("one", "two")
# Python 2: ('one', 'two')
# Python 3: one two
print(configRegistry.get('my/variable'), file=sys.stderr)
# Python 2: SyntaxError
# Python 3: Okay

Using from __future__ import print_function is not allowed as Univention Configuration Registry executes Python code before the template is imported.

The deprecated variable baseConfig has been removed, but configRegistry remains for using.

The API of ConfigRegistry works with str. For Python 2 this equals bytes, while for Python 3 this is a unicode string.

The test case /usr/share/ucs-test/03_ucr/37check-ucr-templates-py3-migration-status.py from the package ucs-test-ucr can be used to check if the UCR template output works with both Python versions and is idempotent.

UCR modules and scripts have no API changes. They simply need to be migrated to be Python 3 compatible.