Custom Options

Custom options are extensions on the compiler's descriptor option messages. Access them through the proto attribute of any descriptor, which holds the raw compiler-generated descriptor message:

from gen.options_pb import ext_sensitive   # an Extension[FieldOptions, bool]

for field in User.desc().fields:
    if field.proto.options is not None and field.proto.options[ext_sensitive]:
        print(f"{field.name} is sensitive")

This works for any descriptor type (DescMessage, DescField, DescEnum, DescService, DescMethod) via their respective proto.options attribute.

How this works

Every descriptor wraps a compiler-generated proto message. The proto attribute gives you direct access to that message, including its options field. Custom options extend those option messages, so reading them is the same as reading any extension:

from gen.options_pb import ext_deprecated_reason   # Extension[MessageOptions, str]

for msg in example_pb.desc().messages:
    if msg.proto.options is None:
        continue
    reason = msg.proto.options[ext_deprecated_reason]
    if reason:
        print(f"{msg.name} is deprecated: {reason}")

Reading options in plugins

The same proto.options pattern works inside a plugin's generate callback; the descriptors in the schema carry the raw compiler messages. See Writing Plugins for a complete example.

See Custom options for the full walkthrough of defining and annotating options.