Adding to_json filter and a test for it.

Author: inhumantsar

jinja2/filters.py

@@ -635,6 +635,12 @@ def do_batch(value, linecount, fill_with=None):
         yield tmp
 
 
+def do_json(value):
+    """A filter that outputs Python objects as JSON"""
+    import json
+    return json.dumps(value)
+
+
 def do_round(value, precision=0, method='common'):
     """Round the number to a given precision. The first
     parameter specifies the precision (default is ``0``), the
@@ -993,4 +999,5 @@ def _select_or_reject(args, kwargs, modfunc, lookup_attr):
     'wordcount':            do_wordcount,
     'wordwrap':             do_wordwrap,
     'xmlattr':              do_xmlattr,
+    'to_json':              do_json,
 }

tests/test_filters.py

@@ -556,3 +556,9 @@ def __init__(self, id, name):
         tmpl = env.from_string('{{ users|rejectattr("id", "odd")|'
                                'map(attribute="name")|join("|") }}')
         assert tmpl.render(users=users) == 'jane'
+
+    def test_json(self, env):
+        env = Environment()
+        obj = ['foo', {'bar': ('baz', None, 1.0, 2)}]
+        tmpl = env.from_string('{{ obj|to_json }}')
+        assert tmpl.render(obj=obj) == '["foo", {"bar": ["baz", null, 1.0, 2]}]'