Merge pull request #60 from ramwin/master

add rightonly jsondiff syntax

.gitignore

@@ -58,4 +58,4 @@ target/
 # PyCharm
 .idea
 
-.hypothesis/
+.hypothesis/

README.rst

@@ -40,6 +40,9 @@ Quickstart
     >>> diff({'a': 1, 'b': 2}, {'b': 3, 'c': 4}, syntax='symmetric')
     {insert: {'c': 4}, 'b': [2, 3], delete: {'a': 1}}
 
+    >>> diff({'list': [1, 2, 3], "poplist": [1, 2, 3]}, {'list': [1, 3]}, syntax="rightonly")
+    {"list": [1, 3], delete: ["poplist"]}
+
     # Special handling of sets
     >>> diff({'a', 'b', 'c'}, {'a', 'c', 'd'})
     {discard: set(['b']), add: set(['d'])}

jsondiff/__init__.py

@@ -342,10 +342,36 @@ def unpatch(self, b, d):
         raise Exception("Invalid symmetric diff")
 
 
+class RightOnlyJsonDiffSyntax(CompactJsonDiffSyntax):
+    """
+    Compare to the CompactJsonDiffSyntax, I will not compare the difference in list,
+    because in some senario we only care about the right value (in most cases means latest value).
+    Instead, I will pop the later list value.
+    """
+
+    def emit_dict_diff(self, a, b, s, added, changed, removed):
+        if s == 1.0:
+            return {}
+        else:
+            changed.update(added)
+            if removed:
+                changed[delete] = list(removed.keys())
+            return changed
+
+    def emit_list_diff(self, a, b, s, inserted, changed, deleted):
+        if s == 0.0:
+            return b
+        elif s == 1.0:
+            return {}
+        else:
+            return b
+
+
 builtin_syntaxes = {
     'compact': CompactJsonDiffSyntax(),
     'symmetric': SymmetricJsonDiffSyntax(),
-    'explicit': ExplicitJsonDiffSyntax()
+    'explicit': ExplicitJsonDiffSyntax(),
+    'rightonly': RightOnlyJsonDiffSyntax(),
 }
 
 

jsondiff/symbols.py

@@ -19,6 +19,7 @@ def __eq__(self, other):
     def __hash__(self) -> int:
         return hash(self.label)
 
+
 missing = Symbol('missing')
 identical = Symbol('identical')
 delete = Symbol('delete')
@@ -55,4 +56,4 @@ def __hash__(self) -> int:
     'left',
     'right',
     '_all_symbols_'
-]
+]

tests/test_jsondiff.py

@@ -1,3 +1,4 @@
+import logging
 import sys
 import unittest
 import pytest
@@ -9,6 +10,15 @@
 from hypothesis import given, settings, strategies
 
 
+logging.basicConfig(
+    level=logging.INFO,
+    format=(
+        '%(asctime)s %(pathname)s[line:%(lineno)d] %(levelname)s %(message)s'
+    ),
+)
+logging.getLogger("jsondiff").setLevel(logging.DEBUG)
+
+
 def generate_scenario(rng):
     a = generate_random_json(rng, sets=True)
     b = perturbate_json(a, rng, sets=True)
@@ -162,3 +172,39 @@ class TestSpecificIssue:
     def test_issue(self,  a, b, syntax, expected):
         actual = diff(a, b, syntax=syntax)
         assert actual == expected
+
+
+class TestRightOnly(unittest.TestCase):
+    def test_right_only_syntax(self):
+        a = {"poplist": [1, 2, 3]}
+        b = {}
+        self.assertEqual(
+            diff(a, b, syntax="rightonly", marshal=True),
+            {
+                "$delete": ["poplist"],
+            }
+        )
+        a = {1: 2, 2: 3, 'list': [1, 2, 3], 'samelist': [1, 2, 3], "poplist": [1, 2, 3]}
+        b = {1: 2, 2: 4, 'list': [1, 3], 'samelist': [1, 2, 3]}
+        self.assertEqual(
+            diff(a, b, syntax="rightonly", marshal=True),
+            {
+                2: 4,
+                "list": [1, 3],
+                "$delete": ["poplist"],
+            }
+        )
+        self.assertEqual(
+            diff(a, b, syntax="rightonly"),
+            {
+                2: 4,
+                "list": [1, 3],
+                delete: ["poplist"],
+            }
+        )
+        c = [1, 2, 3]
+        d = [4, 5, 6]
+        self.assertEqual(
+            diff(c, d, syntax="rightonly", marshal=True),
+            [4, 5, 6],
+        )