ENH: adds logic to handle unary ops on Period

Author: deniederhut

pandas/core/generic.py

@@ -22,6 +22,7 @@
     is_datetime64_dtype,
     is_timedelta64_dtype,
     is_datetime64tz_dtype,
+    is_period_arraylike,
     is_list_like,
     is_dict_like,
     is_re_compilable,
@@ -1031,14 +1032,30 @@ def __neg__(self):
             arr = operator.inv(values)
         elif (is_numeric_dtype(values) or is_timedelta64_dtype(values)):
             arr = operator.neg(values)
+        elif is_period_arraylike(values):
+            # An incredibly terrible workaround that should be replaced
+            # with real logic for handling time period arithmetic
+            if isinstance(self, ABCSeries):
+                freq = self.dt.freq
+                year = min(self.dt.year)
+            elif isinstance(self, ABCDataFrame):
+                freqs = set([self[col].dt.freq for col in self])
+                if len(freqs) > 1:
+                    raise("Unary negative requires Period objects have "
+                          "same frequency, not {}".format(freqs))
+                else:
+                    freq = freqs.pop()
+                    year = min(min([self[col].dt.year for col in self]))
+            unit = Period(value=year, freq=freq)
+            arr = unit - self - 1
         else:
             raise TypeError("Unary negative expects numeric dtype, not {}"
                             .format(values.dtype))
         return self.__array_wrap__(arr)
 
     def __pos__(self):
         values = com._values_from_object(self)
-        if is_bool_dtype(values):
+        if (is_bool_dtype(values) or is_period_arraylike(values)):
             arr = values
         elif (is_numeric_dtype(values) or is_timedelta64_dtype(values)):
             arr = operator.pos(values)