sdk: fix ConsoleSpanExporter

[mauriciovasquezbernal]

19d573a ("Add io and formatter options to console exporter (#412)")
changed the way spans are printed by using write() instead of print().
In Python 3.x sys.stdout is line-buffered, so the spans were not being printed
to the console at the right timing.

This commit fixes that by adding an explicit flush() call at the end of the
export function , it also changes the default formatter to include a line break.

To be precise, only one of the changes was needed to solve the problem, but as
a matter of completness both are included, i.e, to handle the case where the
formatter chosen by the user doesn't append a line break.

Fixes: #448
Supersedes: #451

[codecov-io]

Codecov Report

Merging #455 into master will decrease coverage by 0.14%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #455      +/-   ##
==========================================
- Coverage    88.8%   88.66%   -0.15%     
==========================================
  Files          42       42              
  Lines        2109     2143      +34     
  Branches      238      246       +8     
==========================================
+ Hits         1873     1900      +27     
- Misses        166      170       +4     
- Partials       70       73       +3

Impacted Files	Coverage Δ
...sdk/src/opentelemetry/sdk/trace/export/__init__.py	89.36% <100%> (+0.15%)	⬆️
...dk/src/opentelemetry/sdk/metrics/export/batcher.py	92.5% <0%> (-4.87%)	⬇️
...ry-sdk/src/opentelemetry/sdk/resources/__init__.py	68.18% <0%> (-2.66%)	⬇️
...etry-sdk/src/opentelemetry/sdk/metrics/__init__.py	94.33% <0%> (-2.44%)	⬇️
...ry-ext-wsgi/src/opentelemetry/ext/wsgi/__init__.py	67.59% <0%> (-0.59%)	⬇️
...opentelemetry/sdk/context/propagation/b3_format.py	86.79% <0%> (-0.49%)	⬇️
...lemetry-sdk/src/opentelemetry/sdk/util/__init__.py	85.54% <0%> (-0.35%)	⬇️
...ts/src/opentelemetry/ext/http_requests/__init__.py	89.18% <0%> (-0.29%)	⬇️
...src/opentelemetry/ext/opentracing_shim/__init__.py	95.76% <0%> (-0.18%)	⬇️
...xt-jaeger/src/opentelemetry/ext/jaeger/__init__.py	86.39% <0%> (-0.16%)	⬇️
... and 4 more

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[codeboten]

Nice one, thanks for fixing!

[c24t]

Good catch @mauriciovasquezbernal, thanks!

[c24t]

Consider doing this to avoid two linebreaks for formatters that do end in a newline:

Suggested change

	self.out.write(self.formatter(span))
	self.out.write(endline(self.formatter(span)))

with this in the module:

def endline(line):
    if line.endswith(os.linesep):
        return line
    return line + os.linesep

I haven't checked for windows, but suspect you do want os.linesep here instead of "\n".

[mauriciovasquezbernal]

I'm not totally sure about this one, I think we should let full control to the user, for instance, there could be a case where the user doesn't want to have line breaks at all and use another separator.

I totally agree about the os.linesep, I'm too focus on Linux now 😝

[mauriciovasquezbernal]

Btw, if a formatter ends with a linebreak there would not be two linebreaks, I only adding a linebreak to the default formatter.

[toumorokoshi]

I think agreed to not force lineseps, formatter should control that (and the flush handles this anyway).

[c24t]

Suggested change

	formatter: typing.Callable[[Span], str] = lambda span: str(span)
	+ "\n",
	formatter: typing.Callable[[Span], str] = str,

Along with the other comment suggestion only.

[toumorokoshi]

nice!