DOC/TEST: Add doctest and docs for coerce kwargs.

zipline/utils/input_validation.py

@@ -289,6 +289,15 @@ def coerce(from_, to, **to_kwargs):
     A preprocessing decorator that coerces inputs of a given type by passing
     them to a callable.
 
+    Parameters
+    ----------
+    from : type or tuple or types
+        Inputs types on which to call ``to``.
+    to : function
+        Coercion function to call on inputs.
+    **to_kwargs
+        Additional keywords to forward to every call to ``to``.
+
     Usage
     -----
     >>> @preprocess(x=coerce(float, int), y=coerce(float, int))
@@ -297,6 +306,13 @@ def coerce(from_, to, **to_kwargs):
     ...
     >>> floordiff(3.2, 2.5)
     1
+
+    >>> @preprocess(x=coerce(str, int, base=2), y=coerce(str, int, base=2))
+    ... def add_binary_strings(x, y):
+    ...     return bin(x + y)[2:]
+    ...
+    >>> add_binary_strings('101', '001')
+    '110'
     """
     def preprocessor(func, argname, arg):
         if isinstance(arg, from_):