Support line-delimited JSON

New nodes for handling line-delimited JSON.

https://en.wikipedia.org/wiki/JSON_Streaming

bonobo/_api.py

@@ -2,6 +2,7 @@ import logging
 
 from bonobo.nodes import CsvReader, CsvWriter, FileReader, FileWriter, Filter, JsonReader, JsonWriter, Limit, \
     PickleReader, PickleWriter, PrettyPrinter, RateLimited, Tee, arg0_to_kwargs, count, identity, kwargs_to_arg0, noop
+from bonobo.nodes import LdjsonReader, LdjsonWriter
 from bonobo.strategies import create_strategy
 from bonobo.structs import Bag, ErrorBag, Graph, Token
 from bonobo.util import get_name
@@ -110,6 +111,8 @@ register_api_group(
     Filter,
     JsonReader,
     JsonWriter,
+    LdjsonReader,
+    LdjsonWriter,
     Limit,
     PickleReader,
     PickleWriter,

bonobo/nodes/io/__init__.py

@@ -1,7 +1,7 @@
 """ Readers and writers for common file formats. """
 
 from .file import FileReader, FileWriter
-from .json import JsonReader, JsonWriter
+from .json import JsonReader, JsonWriter, LdjsonReader, LdjsonWriter
 from .csv import CsvReader, CsvWriter
 from .pickle import PickleReader, PickleWriter
 
@@ -12,6 +12,8 @@ __all__ = [
     'FileWriter',
     'JsonReader',
     'JsonWriter',
+    'LdjsonReader',
+    'LdjsonWriter',
     'PickleReader',
     'PickleWriter',
 ]

bonobo/nodes/io/json.py

@@ -45,3 +45,21 @@ class JsonWriter(FileWriter, JsonHandler):
         self._write_line(file, (self.eol if lineno.value else '') + json.dumps(row))
         lineno += 1
         return NOT_MODIFIED
+
+
+class LdjsonReader(FileReader):
+    """Read a stream of JSON objects, one object per line."""
+    loader = staticmethod(json.loads)
+
+    def read(self, fs, file):
+        for line in file:
+            print(line)
+            yield self.loader(line)
+
+
+class LdjsonWriter(FileWriter):
+    """Write a stream of JSON objects, one object per line."""
+    def write(self, fs, file, lineno, **row):
+        lineno += 1  # class-level variable
+        file.write(json.dumps(row) + '\n')
+        return NOT_MODIFIED

docs/changelog.rst

@@ -12,6 +12,11 @@ Command line
 
 * `bonobo download /examples/datasets/coffeeshops.txt` now downloads the coffeeshops example
 
+Graphs and Nodes
+................
+
+* New `LdjsonReader` and `LdjsonWriter` nodes for handling `line-delimited JSON <https://en.wikipedia.org/wiki/JSON_Streaming>`_.
+
 v.0.5.0 - 5 october 2017
 ::::::::::::::::::::::::
 

tests/io/test_json.py

@@ -1,8 +1,9 @@
 import pytest
 
 from bonobo import JsonReader, JsonWriter, settings
+from bonobo import LdjsonReader, LdjsonWriter
 from bonobo.execution.node import NodeExecutionContext
-from bonobo.util.testing import FilesystemTester
+from bonobo.util.testing import FilesystemTester, BufferingNodeExecutionContext
 
 json_tester = FilesystemTester('json')
 json_tester.input_data = '''[{"x": "foo"},{"x": "bar"}]'''
@@ -32,3 +33,32 @@ def test_write_json_kwargs(tmpdir, add_kwargs):
 
     with fs.open(filename) as fp:
         assert fp.read() == '[{"foo": "bar"}]'
+
+
+stream_json_tester = FilesystemTester('json')
+stream_json_tester.input_data = '''{"foo": "bar"}\n{"baz": "boz"}'''
+
+
+def test_read_stream_json(tmpdir):
+    fs, filename, services = stream_json_tester.get_services_for_reader(tmpdir)
+    with BufferingNodeExecutionContext(LdjsonReader(filename),
+                                       services=services) as context:
+        context.write_sync(tuple())
+        actual = context.get_buffer()
+
+    expected = [{"foo": "bar"}, {"baz": "boz"}]
+    assert expected == actual
+
+
+def test_write_stream_json(tmpdir):
+    fs, filename, services = stream_json_tester.get_services_for_reader(tmpdir)
+
+    with BufferingNodeExecutionContext(LdjsonWriter(filename),
+                                       services=services) as context:
+        context.write_sync({'foo': 'bar'})
+        context.write_sync({'baz': 'boz'})
+
+    expected = '''{"foo": "bar"}\n{"baz": "boz"}\n'''
+    with fs.open(filename) as fin:
+        actual = fin.read()
+    assert expected == actual