ENH: Add const per pytoolz#282.

toolz/functoolz.py

@@ -5,7 +5,7 @@
 
 
 __all__ = ('identity', 'thread_first', 'thread_last', 'memoize', 'compose',
-           'pipe', 'complement', 'juxt', 'do', 'curry', 'flip')
+           'pipe', 'complement', 'juxt', 'do', 'curry', 'flip', 'const')
 
 
 def identity(x):
@@ -568,3 +568,23 @@ def flip(func, a, b):
     [1, 2, 3]
     """
     return func(b, a)
+
+
+def const(v):
+    """Return a function that returns v.
+    
+    >>> f = const(5)
+    >>> f()
+    5
+    >>> f(100)
+    5
+    >>> [f(i) for i in range(3)]
+    [5, 5, 5]
+    >>> f('')
+    5
+    >>> f(n=1000)
+    5
+    >>> f(1, 2, 3)
+    5
+    """
+    return lambda *args, **kwargs: v

toolz/tests/test_functoolz.py

@@ -2,7 +2,7 @@
 
 
 from toolz.functoolz import (thread_first, thread_last, memoize, curry,
-                             compose, pipe, complement, do, juxt, flip)
+                             compose, pipe, complement, do, juxt, flip, const)
 from toolz.functoolz import _num_required_args
 from operator import add, mul, itemgetter
 from toolz.utils import raises
@@ -508,3 +508,9 @@ def f(a, b):
         return a, b
 
     assert flip(f, 'a', 'b') == ('b', 'a')
+
+
+def test_const():
+    f = const(5)
+    assert f(100) == 5
+    assert f(100, n=200) == 5