Add select_keys.

doc/source/api.rst

@@ -84,6 +84,7 @@ Dicttoolz
    keymap
    merge
    merge_with
+   select_keys
    update_in
    valfilter
    valmap

toolz/dicttoolz.py

@@ -337,3 +337,22 @@ def get_in(keys, coll, default=None, no_default=False):
         if no_default:
             raise
         return default
+
+
+def select_keys(keys, d, factory=dict):
+    """ Select only certain keys from a dictionary
+
+    If supplied keys are not found in the dictionary, returns an empty
+    dictionary.
+
+    >>> d = {'a': 1, 'b': 2, 'c': 3}
+    >>> select_keys(['a', 'b', 'd'], d)  # doctest: +SKIP
+    {'a': 1, 'b': 2}
+    >>> select_keys(['d'], d)
+    {}
+    """
+    rv = factory()
+    for k in keys:
+        if k in d:
+            rv[k] = d[k]
+    return rv

toolz/tests/test_dicttoolz.py

@@ -1,10 +1,11 @@
+import os
 from collections import defaultdict as _defaultdict
 from collections.abc import Mapping
-import os
-from toolz.dicttoolz import (merge, merge_with, valmap, keymap, update_in,
-                             assoc, dissoc, keyfilter, valfilter, itemmap,
-                             itemfilter, assoc_in)
 from toolz.functoolz import identity
+from toolz.dicttoolz import (assoc, assoc_in, dissoc, itemfilter,
+                             itemmap, keyfilter, keymap, merge,
+                             merge_with, select_keys, update_in,
+                             valfilter, valmap)
 from toolz.utils import raises
 
 
@@ -119,6 +120,14 @@ def test_assoc_in(self):
         assert d is oldd
         assert d2 is not oldd
 
+    def test_select_keys(self):
+        D, kw = self.D, self.kw
+        assert select_keys([], D({}), **kw) == D({})
+        assert select_keys(["a"], D({"a": 1}), **kw) == D({"a": 1})
+        assert select_keys([], D({"a": 1}), **kw) == D({})
+        assert select_keys(["b"], D({"a": 1}), **kw) == D({})
+        assert select_keys(["b"], D({"a": 1, "b": 2}), **kw) == D({"b": 2})
+
     def test_update_in(self):
         D, kw = self.D, self.kw
         assert update_in(D({"a": 0}), ["a"], inc, **kw) == D({"a": 1})