Pick by

README.md

@@ -582,7 +582,7 @@ R.pick(['v1'], obj) # {'v1': 1}
 R.pickAll(['v1', 'v3'], obj) # {'v1': 1, 'v3': None}
 ```
 
-- [ ] pickBy
+- [x] pickBy
 - [x] 0.1.2 pipe
 - [ ] pipeWith
 - [x] 0.1.2 pluck

ramda/__init__.py

@@ -97,6 +97,7 @@
 from .paths import paths
 from .pick import pick
 from .pickAll import pickAll
+from .pickBy import pickBy
 from .pipe import pipe
 from .pluck import pluck
 from .prepend import prepend

ramda/pickBy.py

@@ -0,0 +1,20 @@
+from .private._curry2 import _curry2
+from .private._inspect import funcArgsLength
+
+
+def inner_pickBy(test, obj):
+  result = {}
+  for key in obj:
+    if funcArgsLength(test) <= 1:
+      if test(obj[key]):
+        result[key] = obj[key]
+    if funcArgsLength(test) == 2:
+      if test(obj[key], key):
+        result[key] = obj[key]
+    if funcArgsLength(test) == 3:
+      if test(obj[key], key, obj):
+        result[key] = obj[key]
+  return result
+
+
+pickBy = _curry2(inner_pickBy)

test/test_pickBy.py

@@ -0,0 +1,40 @@
+import unittest
+
+import ramda as R
+
+"""
+https://github.com/ramda/ramda/blob/master/test/pickBy.js
+"""
+
+obj = {'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5, 'f': 6}
+
+
+class TestPickBy(unittest.TestCase):
+  def test_create_a_copy_of_the_object(self):
+    self.assertEqual(obj, R.pickBy(R.always(True), obj))
+
+  def test_when_returning_truth_keeps_the_key(self):
+    self.assertEqual(obj, R.pickBy(R.T, obj))
+    self.assertEqual(obj, R.pickBy(R.always({'a': 1}), obj))
+    self.assertEqual(obj, R.pickBy(R.always(1), obj))
+
+  def test_when_returning_falsy_do_not_keep_the_key(self):
+    self.assertEqual({}, R.pickBy(R.F, obj))
+    self.assertEqual({}, R.pickBy(R.always({}), obj))
+    self.assertEqual({}, R.pickBy(R.always(0), obj))
+    self.assertEqual({}, R.pickBy(R.always(None), obj))
+
+  def test_is_called_with_val_key_obj(self):
+    def pred(val, key, _obj):
+      self.assertEqual(obj, _obj)
+      return key == 'd' and val == 4
+    self.assertEqual({'d': 4}, R.pickBy(pred, obj))
+
+  def test_first_method_has_2_param(self):
+    def pred(val, key):
+      return key == 'd' and val == 4
+    self.assertEqual({'d': 4}, R.pickBy(pred, obj))
+
+
+if __name__ == '__main__':
+  unittest.main()