ENH: Adds a const function to functoolz

toolz/functoolz.py

@@ -568,3 +568,22 @@ def flip(func, a, b):
     [1, 2, 3]
     """
     return func(b, a)
+
+
+def const(value):
+    """Create a constant function. A constant function is a function
+    that returns the same value for all inputs.
+
+    >>> c = const(1)
+    >>> type(c)
+    >>> c(2)
+    1
+    >>> c(3)
+    1
+    >>> c('a', 'b', kwarg='c')
+    1
+    """
+    def constant_function(*args, **kwargs):
+        return value
+
+    return constant_function

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 +508,15 @@ def f(a, b):
         return a, b
 
     assert flip(f, 'a', 'b') == ('b', 'a')
+
+
+def test_const():
+    c = const(1)
+
+    for n in range(10):
+        assert c(n) == 1
+
+    for arg in 'abcdefghij':
+        assert c(n) == 1
+
+    assert c(1, 2, *(3, 4), kwarg=5, **{'kw': 6})