Add io and formatter options to console exporter (open-telemetry#412)

Co-authored-by: Diego Hurtado <ocelotl@users.noreply.github.com>

Author: c24t

opentelemetry-sdk/src/opentelemetry/sdk/trace/export/__init__.py

@@ -14,6 +14,7 @@
 
 import collections
 import logging
+import sys
 import threading
 import typing
 from enum import Enum
@@ -266,7 +267,15 @@ class ConsoleSpanExporter(SpanExporter):
     spans to the console STDOUT.
     """
 
+    def __init__(
+        self,
+        out: typing.IO = sys.stdout,
+        formatter: typing.Callable[[Span], str] = str,
+    ):
+        self.out = out
+        self.formatter = formatter
+
     def export(self, spans: typing.Sequence[Span]) -> SpanExportResult:
         for span in spans:
-            print(span)
+            self.out.write(self.formatter(span))
         return SpanExportResult.SUCCESS

opentelemetry-sdk/tests/trace/export/test_export.py

@@ -276,3 +276,31 @@ def test_batch_span_processor_parameters(self):
             max_queue_size=256,
             max_export_batch_size=512,
         )
+
+
+class TestConsoleSpanExporter(unittest.TestCase):
+    def test_export(self):  # pylint: disable=no-self-use
+        """Check that the console exporter prints spans."""
+        exporter = export.ConsoleSpanExporter()
+
+        # Mocking stdout interferes with debugging and test reporting, mock on
+        # the exporter instance instead.
+        span = trace.Span("span name", mock.Mock())
+        with mock.patch.object(exporter, "out") as mock_stdout:
+            exporter.export([span])
+        mock_stdout.write.assert_called_once_with(str(span))
+        self.assertEqual(mock_stdout.write.call_count, 1)
+
+    def test_export_custom(self):  # pylint: disable=no-self-use
+        """Check that console exporter uses custom io, formatter."""
+        mock_span_str = mock.Mock(str)
+
+        def formatter(span):  # pylint: disable=unused-argument
+            return mock_span_str
+
+        mock_stdout = mock.Mock()
+        exporter = export.ConsoleSpanExporter(
+            out=mock_stdout, formatter=formatter
+        )
+        exporter.export([trace.Span("span name", mock.Mock())])
+        mock_stdout.write.assert_called_once_with(mock_span_str)