Add functoolz.reorder_args

toolz/curried/__init__.py

@@ -88,6 +88,7 @@
 reduce = toolz.curry(toolz.reduce)
 reduceby = toolz.curry(toolz.reduceby)
 remove = toolz.curry(toolz.remove)
+reorder_args = toolz.curry(toolz.reorder_args)
 sliding_window = toolz.curry(toolz.sliding_window)
 sorted = toolz.curry(toolz.sorted)
 tail = toolz.curry(toolz.tail)

toolz/functoolz.py

@@ -1,7 +1,7 @@
-from functools import reduce, partial
+from functools import reduce, partial, wraps
 import inspect
 import sys
-from operator import attrgetter, not_
+from operator import itemgetter, attrgetter, not_
 from importlib import import_module
 from types import MethodType
 
@@ -12,7 +12,7 @@
 
 __all__ = ('identity', 'apply', 'thread_first', 'thread_last', 'memoize',
            'compose', 'compose_left', 'pipe', 'complement', 'juxt', 'do',
-           'curry', 'flip', 'excepts')
+           'curry', 'flip', 'excepts', 'reorder_args')
 
 PYPY = hasattr(sys, 'pypy_version_info')
 
@@ -731,6 +731,42 @@ def flip(func, a, b):
     return func(b, a)
 
 
+def reorder_args(func, new_args):
+    """ Returns a new function with a desired argument order.
+
+    >>> def op(a, b, c):
+    ...    return a // (b - c)
+    ...
+    >>> new_op = reorder_args(op, ('c', 'a', 'b'))
+    >>> new_op(1, 2, 3) == op(2, 3, 1)
+    True
+    """
+    func_sig = inspect.signature(func)
+    arg_map = []
+    parameters = [None] * len(func_sig.parameters)
+    for i, arg in enumerate(func_sig.parameters.values()):
+        if (arg.kind in {inspect.Parameter.POSITIONAL_ONLY, 
+                         inspect.Parameter.VAR_POSITIONAL, 
+                         inspect.Parameter.POSITIONAL_OR_KEYWORD}
+                and arg.default is inspect._empty):
+            try:
+                new_ind = new_args.index(arg.name)
+                arg_map.append(new_ind)
+                parameters[new_ind] = arg
+            except ValueError:
+                raise ValueError(f"Unable to find positional argument `{arg.name}` in signature for `{func.__name__}`")
+        else:
+            parameters[i] = arg
+
+    _mapper = itemgetter(*arg_map)
+    @wraps(func)
+    def wrapper(*args, **kwargs):
+        return func(*_mapper(args), **kwargs)
+
+    wrapper.__signature__ = func_sig.replace(parameters=parameters)
+    return wrapper
+
+
 def return_none(exc):
     """ Returns None.
     """

toolz/tests/test_functoolz.py

@@ -2,8 +2,8 @@
 import toolz
 from toolz.functoolz import (thread_first, thread_last, memoize, curry,
                              compose, compose_left, pipe, complement, do, juxt,
-                             flip, excepts, apply)
-from operator import add, mul, itemgetter
+                             flip, excepts, apply, reorder_args)
+from operator import add, mul, getitem, itemgetter
 from toolz.utils import raises
 from functools import partial
 
@@ -794,3 +794,17 @@ def raise_(a):
     excepting = excepts(object(), object(), object())
     assert excepting.__name__ == 'excepting'
     assert excepting.__doc__ == excepts.__doc__
+
+
+def test_reorder_args():
+    def op(a, b, c, d=1):
+        return a // (b - c) + d
+
+    new_op = reorder_args(op, ('c', 'a', 'b'))
+    assert new_op(1, 2, 3, d=1) == op(2, 3, 1, d=1)
+
+    # test builtin functions (ie C functions)
+    getflip = reorder_args(getitem, ('b', 'a'))
+    get1 = curry(getflip, 1)
+    assert get1([1, 2, 3, 1, 1]) == 2
+