AVRO-3065: Introduce UUID logical type to Python implementation

[subhashb]

This PR introduces the UUID logical type implementation that was missing in the
primary python implementation. A new UUIDSchema has been introduced that
validates for valid UUID4 string values.

Closes: https://issues.apache.org/jira/browse/AVRO-3065

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Jira

• My PR addresses the following Avro Jira issues and references them in the PR title. For example, "AVRO-3065: Add support for uuid logical type to Python implementation"
  • https://issues.apache.org/jira/browse/AVRO-3065
  • In case you are adding a dependency, check if the license complies with the ASF 3rd Party License Policy.

Tests

• My PR adds the following unit tests:
  • Test for valid UUID Logical Type in Schema
  • Test for valid UUID in values

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  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

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[RyanSkraba]

For the test case, should this be:

Suggested change

	('{"type": "string", "logicalType": "uuid"}', u'570feebe-2bbc-4937-98df-285944e1dbbd'),
	('{"type": "string", "logicalType": "uuid"}', uuid.UUID('570feebe-2bbc-4937-98df-285944e1dbbd')),

I'm not sure if this suggestion is correct, but it's what I would expect once UUID logical type is implemented!

Since this is a new feature, should we go with the expectation that the in-memory representation of a UUID datum is a UUID object instead of a string? Should we accept either/or when serializing, but always deserialize to one or the other? What do you think?

[RyanSkraba]

Thanks for taking this on!

My comment on the test case is that if we're (finally!) introducing the UUID type to python, we might use the uuid type for these data (like we use datetime instances for the date and time logical types).

This could break code for developers that have schemas with uuid logical types and are happy to treat them as strings for now, though. Much like using avro-1.7.7 would happily ignore date logical types and treat them as ints...

If we decide there's no real advantage to using uuid instances, this looks good though!

[subhashb]

Hey @RyanSkraba!

Thank you for the review.

Yes, I was thinking primarily about backward compatibility when I represented UUID as a string.

Some aspects (and past experiences) that made string representation a better option for me:

• UUID objects are not serializable by default.
• A project persisting objects (with a UUID logical field) from Avro today will need to be enhanced to handle UUID objects (you mentioned this too) manually
• Marshmallow's UUID field accepts a string but always returns a UUID object
• Django has a UUID Field, but Postgres is the only database with native UUID data type support. Rest interpret the value as a string. Using the Django UUID field still requires you to generate the UUID yourself.
• SQLAlchemy treats UUIDs as strings and needs as_uuid=True to explicitly treat the value as a UUID object.

Having said that, UUID object representation might be a better long-term option. Please let me know what you think.

[subhashb]

f7ec849 updates the validation to accept UUIDs of different versions, instead of being locked to version 4.

[RyanSkraba]

Thanks for the explanation -- your reasoning is sound. Especially since the uuid package doesn't really add a lot of functionality over strings (in comparison to using datetime instances over numbers).

[RyanSkraba]

Hey, if nobody has any other comments, let's just merge this! Thanks for the contribution!