BUG: GH4080, int conversion of underlying series to float needs updating in parent frame

doc/source/release.rst

@@ -318,6 +318,8 @@ pandas 0.12
     iterated over when regex=False (:issue:`4115`)
   - Fixed bug in ``convert_objects(convert_numeric=True)`` where a mixed numeric and
     object Series/Frame was not converting properly (:issue:`4119`)
+  - Bug in Series update where the parent frame is not updating its blocks based on
+    dtype changes (:issue:`4080`)
 
 
 pandas 0.11.0

pandas/core/generic.py

@@ -1,5 +1,6 @@
 # pylint: disable=W0231,E1101
 
+import weakref
 import numpy as np
 import pandas.lib as lib
 from pandas.core.base import PandasObject
@@ -667,11 +668,17 @@ def _get_item_cache(self, item):
             values = self._data.get(item)
             res = self._box_item_values(item, values)
             cache[item] = res
+            res._cacher  = (item,weakref.ref(self))
             return res
 
     def _box_item_values(self, key, values):
         raise NotImplementedError
 
+    def _maybe_cache_changed(self, item, value):
+        """ the object has called back to us saying
+        maybe it has changed """
+        self._data.maybe_changed(item, value)
+
     def _clear_item_cache(self):
         self._item_cache.clear()
 

pandas/core/internals.py

@@ -1554,6 +1554,12 @@ def _interleave(self, items):
 
         return result
 
+    def maybe_changed(self, item, value):
+        """ our obj may have changed dtype """
+        current = self.get(item)
+        if current.dtype != value.dtype:
+            self.set(item, value)
+
     def xs(self, key, axis=1, copy=True):
         if axis < 1:
             raise AssertionError('Can only take xs across axis >= 1, got %d'

pandas/core/series.py

@@ -557,6 +557,12 @@ def __setstate__(self, state):
         self.index = _handle_legacy_indexes([index])[0]
         self.name = name
 
+    def _maybe_update_cacher(self):
+        """ see if we need to update our parent cacher """
+        cacher = getattr(self,'_cacher',None)
+        if cacher is not None:
+            cacher[1]()._maybe_cache_changed(cacher[0],self)
+
     # indexers
     @property
     def axes(self):
@@ -2157,7 +2163,8 @@ def update(self, other):
         """
         other = other.reindex_like(self)
         mask = notnull(other)
-        com._maybe_upcast_putmask(self.values,mask,other,change=self.values)
+        com._maybe_upcast_putmask(self.values,mask,other,change=self)
+        self._maybe_update_cacher()
 
     #----------------------------------------------------------------------
     # Reindexing, sorting

pandas/tests/test_frame.py

@@ -8707,6 +8707,16 @@ def test_update_dtypes(self):
                              columns=['A','B','bool1','bool2'])
         assert_frame_equal(df, expected)
 
+        # GH 4080, int conversions
+        df = DataFrame(dict((c, [1,2,3]) for c in ['a', 'b', 'c']))
+        df.set_index(['a', 'b', 'c'], inplace=True)
+        s = Series([1], index=[(2,2,2)])
+        df['val'] = 0
+        df['val'].update(s)
+        expected = DataFrame(dict(a = [1,2,3], b = [1,2,3], c = [1,2,3], val = [0.0,1.0,0.0]))
+        expected.set_index(['a', 'b', 'c'], inplace=True)
+        assert_frame_equal(df,expected)
+
     def test_update_nooverwrite(self):
         df = DataFrame([[1.5, nan, 3.],
                         [1.5, nan, 3.],