Added JSON stream generator for extending local parser backend.

.gitignore

@@ -6,4 +6,5 @@ __pycache__
 data
 .dependencies/
 .volumes/
-.pytest_cache/
\ No newline at end of file
+.pytest_cache/
+.coverage

nomad/parsing.py

+import json
+
+
+class JSONStreamGenerator():
+    """
+    A generator that allows to output JSON based on calling 'event' functions.
+    Its pure python and could be replaced by some faster implementation, e.g. yajl-py.
+    It does not do anychecks. Expect random exceptions when events are out of order or
+    imcomplete.
+    """
+    def __init__(self, fp, pretty=False):
+        self._fp = fp
+        self._pretty = pretty
+
+        self._indent = ''
+        self._separators = ['']
+
+    def _write(self, str):
+        self._fp.write(str)
+
+    def _write_seperator(self):
+        self._write(self._separators.pop())
+
+    def _seperator_with_newline(self, base=None):
+        pretty_ext = ('\n%s' % self._indent) if self._pretty else ''
+        if base is None:
+            return pretty_ext
+        else:
+            return '%s%s' % (base, pretty_ext)
+
+    def _open(self, open_char):
+        self._write_seperator()
+        self._write(open_char)
+        self._indent = '%s  ' % self._indent
+        self._separators.append(self._seperator_with_newline())
+
+    def _close(self, close_char):
+        self._separators.pop()
+        self._indent = self._indent[:-2]
+        self._write(self._seperator_with_newline())
+        self._write(close_char)
+        self._separators.append(self._seperator_with_newline(','))
+
+    def open_object(self):
+        self._open('{')
+
+    def close_object(self):
+        self._close('}')
+
+    def open_array(self):
+        self._open('[')
+
+    def close_array(self):
+        self._close(']')
+
+    def key_value(self, key, value):
+        self.key(key)
+        self.value(value)
+
+    def key(self, key):
+        self._write_seperator()
+        json.dump(key, self._fp)
+        self._separators.append(': ' if self._pretty else ':')
+
+    def value(self, value):
+        self._write_seperator()
+        json.dump(value, self._fp)
+        self._separators.append(self._seperator_with_newline(','))

tests/test_parsing.py

+from nomad.parsing import JSONStreamGenerator
+from io import StringIO
+import json
+import pytest
+
+
+def create_reference(data, pretty):
+    if (pretty):
+        return json.dumps(data, indent=2)
+    else:
+        return json.dumps(data, separators=(',', ':'))
+
+
+@pytest.mark.parametrize("pretty", [False, True])
+def test_stream_generator(pretty):
+    example_data = [
+        {
+            'key1': 'value',
+            'key2': 1
+        },
+        {
+            'key': {
+                'key': 'value'
+            }
+        }
+    ]
+
+    out = StringIO()
+    generator = JSONStreamGenerator(out, pretty=pretty)
+    generator.open_array()
+    generator.open_object()
+    generator.key('key1')
+    generator.value('value')
+    generator.key('key2')
+    generator.value(1)
+    generator.close_object()
+    generator.open_object()
+    generator.key('key')
+    generator.open_object()
+    generator.key('key')
+    generator.value('value')
+    generator.close_object()
+    generator.close_object()
+    generator.close_array()
+
+    assert create_reference(example_data, pretty) == out.getvalue()
+