move MergeError to pandas/errors

Author: Nick Eubank

pandas/core/reshape/merge.py

@@ -40,6 +40,7 @@
 import pandas.core.algorithms as algos
 import pandas.core.common as com
 from pandas._libs import hashtable as libhashtable, join as libjoin, lib
+from pandas.errors import MergeError
 
 
 @Substitution('\nleft : DataFrame')
@@ -60,10 +61,6 @@ def merge(left, right, how='inner', on=None, left_on=None, right_on=None,
     merge.__doc__ = _merge_doc % '\nleft : DataFrame'
 
 
-class MergeError(ValueError):
-    pass
-
-
 def _groupby_and_merge(by, on, left, right, _merge_pieces,
                        check_duplicates=True):
     """

pandas/errors/__init__.py

@@ -57,3 +57,9 @@ class ParserWarning(Warning):
     """
 
 
+class MergeError(ValueError):
+    """
+    Error raised when problems arise during merging due to problems
+    with input data. Subclass of `ValueError`.
+
+    """