CLN: Improve Exceptions in core/frame and testing in test_frame and test_multilievel

doc/source/release.rst

@@ -71,8 +71,9 @@ pandas 0.13
     when the key is a column
   - Support for using a ``DatetimeIndex/PeriodsIndex`` directly in a datelike calculation
     e.g. s-s.index (:issue:`4629`)
-  - Better/cleaned up exceptions in core/common, io/excel and core/format.
-    (:issue:`4721`, :issue:`3954`)
+  - Better/cleaned up exceptions in core/common, io/excel and core/format
+    (:issue:`4721`, :issue:`3954`), as well as cleaned up test cases in
+    tests/test_frame, tests/test_multilevel (:issue:`4732`).
 
 **API Changes**
 
@@ -143,9 +144,10 @@ pandas 0.13
       now returns a ``MultiIndex`` rather than an ``Index``. (:issue:`4039`)
 
   - Infer and downcast dtype if ``downcast='infer'`` is passed to ``fillna/ffill/bfill`` (:issue:`4604`)
-  - Factored out excel_value_to_python_value from ExcelFile::_parse_excel (:issue:`4589`)
   - ``__nonzero__`` for all NDFrame objects, will now raise a ``ValueError``, this reverts back to (:issue:`1073`, :issue:`4633`)
     behavior.
+  - ``DataFrame.update()`` no longer raises a ``DataConflictError``, it now
+    will raise a ``ValueError`` instead (if necessary) (:issue:`4732`)
 
 **Internal Refactoring**
 

pandas/compat/__init__.py

@@ -665,6 +665,25 @@ def __and__(self, other):
 else:
     from collections import OrderedDict, Counter
 
+if PY3:
+    def raise_with_traceback(exc, traceback=Ellipsis):
+        if traceback == Ellipsis:
+            _, _, traceback = sys.exc_info()
+        raise exc.with_traceback(traceback)
+else:
+    # this version of raise is a syntax error in Python 3
+    exec("""
+def raise_with_traceback(exc, traceback=Ellipsis):
+    if traceback == Ellipsis:
+        _, _, traceback = sys.exc_info()
+    raise exc, None, traceback
+""")
+
+raise_with_traceback.__doc__ = (
+"""Raise exception with existing traceback.
+If traceback is not passed, uses sys.exc_info() to get traceback."""
+)
+
 # http://stackoverflow.com/questions/4126348
 # Thanks to @martineau at SO
 

pandas/core/format.py

@@ -825,9 +825,8 @@ def __init__(self, obj, path_or_buf, sep=",", na_rep='', float_format=None,
 
         # validate mi options
         if self.has_mi_columns:
-            # guarded against in to_csv itself
-            if cols is not None: # pragma: no cover
-                raise AssertionError("cannot specify cols with a multi_index on the columns")
+            if cols is not None:
+                raise TypeError("cannot specify cols with a MultiIndex on the columns")
 
         if cols is not None:
             if isinstance(cols,Index):