Issue with explicit_end set to False having no impact on small dump

[daniel-o-jones]

The following code leads to unexpected results
import yaml

print(yaml.dump(False, explicit_end=False))
print(yaml.dump(False, explicit_end=True))

Changing explicit_end results in no difference in output, with both printing three full stops and a new line after False.

print(yaml.dump({'key': False}, explicit_end=False))
print(yaml.dump({'key': False}, explicit_end=True))

Here changing explicit_end does result in a difference in output, with the former not printing the three full stops and newline.

Is this the desired behaviour?

[perlpunk]

The reason for that is, that a YAML document with only a plain scalar is considered "open-ended", and therefor needs an explicit document-end. So in this case the option is ignored.

This is important because of the YAML 1.1 specification, which allows concatenating documents
with a directive without the ...:

%YAML 1.1
--- "foo"
%YAML 1.1
--- "bar"

but for plain scalars the ... is needed:

%YAML 1.1
--- foo
...
%YAML 1.1
--- bar

YAML 1.2 does not allow the first example, and I would actually like to change the PyYAML behaviour to YAML 1.2, so that ignoring the option would not be necessary anymore. But that needs thorough testing.

[aldpuzz]

I digged a bit into this issue and found that it's this block which causes the problem in print(yaml.dump(True, explicit_start =False, explicit_end=False)) case.

yaml/emitter.py:

        elif isinstance(self.event, StreamEndEvent):
            if self.open_ended:
                self.write_indicator('...', True)
                self.write_indent()
            self.write_stream_end()
            self.state = self.expect_nothing

It seems that DocumentEndEvent is correctly handled (it contains an explicit attribute) while StreamEndEvent is not, It simply doesn't know about the user's request of explicit_end=True. I wonder if adding the explicit attribute to StreamEndEvent would be "good style":