Merge pull request #213 from kwmsmith/promote-refactor

Refactor promote to correctly handle `string` and `?string`.

datashape/promote.py

@@ -12,7 +12,7 @@ def promote(lhs, rhs, promote_option=True):
 
     Examples
     --------
-    >>> from datashape import int32, int64, Option
+    >>> from datashape import int32, int64, Option, string
     >>> x = Option(int32)
     >>> y = int64
     >>> promote(x, y)
@@ -24,25 +24,34 @@ def promote(lhs, rhs, promote_option=True):
     >>> promote(x, y, promote_option=False)
     ctype("int64")
 
+    Strings are handled differently than NumPy, which promotes to ctype("object")
+    >>> x = string
+    >>> y = Option(string)
+    >>> promote(x, y) == promote(y, x) == Option(string)
+    True
+    >>> promote(x, y, promote_option=False)
+    ctype("string")
+
     Notes
     ----
-    This uses ``numpy.result_type`` for type promotion logic.  See the numpy
-    documentation at
+    Except for ``datashape.string`` types, this uses ``numpy.result_type`` for
+    type promotion logic.  See the numpy documentation at:
+
     http://docs.scipy.org/doc/numpy/reference/generated/numpy.result_type.html
     """
     if lhs == rhs:
         return lhs
+    left, right = getattr(lhs, 'ty', lhs), getattr(rhs, 'ty', rhs)
+    if left == right == datashape.string:
+        # Special case string promotion, since numpy promotes to `object`.
+        dtype = datashape.string
     else:
-        left, right = getattr(lhs, 'ty', lhs), getattr(rhs, 'ty', rhs)
-        dtype = datashape.CType.from_numpy_dtype(
-            np.result_type(
-                datashape.to_numpy_dtype(left),
-                datashape.to_numpy_dtype(right),
-            ),
-        )
-        if promote_option:
-            dtype = optionify(lhs, rhs, dtype)
-        return dtype
+        np_res_type = np.result_type(datashape.to_numpy_dtype(left),
+                                     datashape.to_numpy_dtype(right))
+        dtype = datashape.CType.from_numpy_dtype(np_res_type)
+    if promote_option:
+        dtype = optionify(lhs, rhs, dtype)
+    return dtype
 
 
 def optionify(lhs, rhs, dshape):

datashape/tests/test_promote.py

@@ -1,5 +1,7 @@
-from datashape import promote, Option, float64, int64, float32, optionify
+import pytest
 
+from datashape import (promote, Option, float64, int64, float32, optionify,
+                       string, datetime_ as datetime)
 
 def test_simple():
     x = int64
@@ -27,3 +29,61 @@ def test_option_in_parent():
     y = Option(float32)
     z = optionify(x, y, y)
     assert z == y
+
+
+@pytest.mark.parametrize('x,y,p,r',
+                         [[string, string, True, string],
+                          [string, string, False, string],
+
+                          [Option(string),
+                           Option(string),
+                           True,
+                           Option(string)],
+
+                          [Option(string),
+                           Option(string),
+                           False,
+                           Option(string)],
+
+                          [Option(string),
+                           string,
+                           True,
+                           Option(string)],
+
+                          [Option(string),
+                           string,
+                           False,
+                           string]])
+def test_promote_string_with_option(x, y, p, r):
+    assert (promote(x, y, promote_option=p) ==
+            promote(y, x, promote_option=p) ==
+            r)
+
+
+@pytest.mark.parametrize('x,y,p,r',
+                         [[datetime, datetime, True, datetime],
+                          [datetime, datetime, False, datetime],
+
+                          [Option(datetime),
+                           Option(datetime),
+                           True,
+                           Option(datetime)],
+
+                          [Option(datetime),
+                           Option(datetime),
+                           False,
+                           Option(datetime)],
+
+                          [Option(datetime),
+                           datetime,
+                           True,
+                           Option(datetime)],
+
+                          [Option(datetime),
+                           datetime,
+                           False,
+                           datetime]])
+def test_promote_datetime_with_option(x, y, p, r):
+    assert (promote(x, y, promote_option=p) ==
+            promote(y, x, promote_option=p) ==
+            r)

docs/source/whatsnew/0.5.1.txt

@@ -7,11 +7,7 @@ Release |version|
 New Features
 ------------
 
-* Adds :func:`~datashape.discover` support for :class:`types.MappingProxyType`
-  objects in python 3 and :class:`types.DictProxyType` in python 2
-  (:issue:`212`).
-* Adds :func:`~datashape.discover` support for :class:`collections.OrderedDict`
-  objects (:issue:`212`).
+None
 
 New Types
 ---------

docs/source/whatsnew/0.5.2.txt

@@ -0,0 +1,44 @@
+Release |version|
+-----------------
+
+:Release: |version|
+:Date: TBD
+
+New Features
+------------
+
+* Adds :func:`~datashape.discover` support for :class:`types.MappingProxyType`
+  objects in python 3 and :class:`types.DictProxyType` in python 2
+  (:issue:`212`).
+* Adds :func:`~datashape.discover` support for :class:`collections.OrderedDict`
+  objects (:issue:`212`).
+
+New Types
+---------
+
+None
+
+Experimental Types
+------------------
+
+.. warning::
+
+   Experimental types are subject to change.
+
+None
+
+API Changes
+-----------
+
+None
+
+Bug Fixes
+---------
+
+* Fixes :func:`~datashape.promote` to handle :class:`~datashape.string` types
+  correctly when mixing with :class:`~datashape.Option` types (:issue:`213`).
+
+Miscellaneous
+-------------
+
+None