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})