Implement a json formatter in cliff

This change replaces the cliff-tablib json formatter with an internal
replacement. It differs from the tablib formatter in the following ways:
- by default outputs with an indent of 2 spaces. The --noindent formatting
  argument outputs with no indentation, to save space or to pipe to tools
  which can't handle multi-line input.
- emit_one serialises a simple dict where the column name is the key
and the data item is the value (rather than a list of dicts with
'Field' and 'Value' keys)

The cliff release which contains this change will need a corresponding
cliff-tablib release which removes the json formatter from its setup.py
entry_points.

Change-Id: I7f9b1f339d96ead347a0c9d95ec7004a78d8c9d5
Related-Bug: #1308744

1 files changed, 30 insertions, 0 deletions

diff --git a/cliff/formatters/json_format.py b/cliff/formatters/json_format.py
new file mode 100644
index 0000000..fc35da1
--- /dev/null
+++ b/cliff/formatters/json_format.py
@@ -0,0 +1,30 @@
+"""Output formatters for JSON.
+"""
+
+import json
+
+from .base import ListFormatter, SingleFormatter
+
+
+class JSONFormatter(ListFormatter, SingleFormatter):
+
+    def add_argument_group(self, parser):
+        group = parser.add_argument_group(title='json formatter')
+        group.add_argument(
+            '--noindent',
+            action='store_true',
+            dest='noindent',
+            help='whether to disable indenting the JSON'
+        )
+
+    def emit_list(self, column_names, data, stdout, parsed_args):
+        items = []
+        for item in data:
+            items.append(dict(zip(column_names, item)))
+        indent = None if parsed_args.noindent else 2
+        json.dump(items, stdout, indent=indent)
+
+    def emit_one(self, column_names, data, stdout, parsed_args):
+        one = dict(zip(column_names, data))
+        indent = None if parsed_args.noindent else 2
+        json.dump(one, stdout, indent=indent)