change merge validate errors to MergeError from ValueError, 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):
  """
@@ -986,23 +983,23 @@ def _validate(self, validate):
  # Check data integrity
  if validate in ["one_to_one", "1:1"]:
  if not left_unique and not right_unique:
- raise ValueError("Merge keys are not unique in either left"
+ raise MergeError("Merge keys are not unique in either left"
  " or right dataset; not a one-to-one merge")
  elif not left_unique:
- raise ValueError("Merge keys are not unique in left dataset;"
+ raise MergeError("Merge keys are not unique in left dataset;"
  " not a one-to-one merge")
  elif not right_unique:
- raise ValueError("Merge keys are not unique in right dataset;"
+ raise MergeError("Merge keys are not unique in right dataset;"
  " not a one-to-one merge")
 
  elif validate in ["one_to_many", "1:m"]:
  if not left_unique:
- raise ValueError("Merge keys are not unique in left dataset;"
+ raise MergeError("Merge keys are not unique in left dataset;"
  "not a one-to-many merge")
 
  elif validate in ["many_to_one", "m:1"]:
  if not right_unique:
- raise ValueError("Merge keys are not unique in right dataset;"
+ raise MergeError("Merge keys are not unique in right dataset;"
  " not a many-to-one merge")
 
  elif validate in ['many_to_many', 'm:m']:

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`.
+
+ """

pandas/tests/reshape/test_merge.py

@@ -789,11 +789,11 @@ def test_validation(self):
  merge(left, right_w_dups, left_index=True, right_index=True,
  validate='one_to_many')
 
- with pytest.raises(ValueError):
+ with pytest.raises(MergeError):
  merge(left, right_w_dups, left_index=True, right_index=True,
  validate='one_to_one')
 
- with pytest.raises(ValueError):
+ with pytest.raises(MergeError):
  merge(left, right_w_dups, on='a', validate='one_to_one')
 
  # Dups on left
@@ -802,21 +802,21 @@ def test_validation(self):
  merge(left_w_dups, right, left_index=True, right_index=True,
  validate='many_to_one')
 
- with pytest.raises(ValueError):
+ with pytest.raises(MergeError):
  merge(left_w_dups, right, left_index=True, right_index=True,
  validate='one_to_one')
 
- with pytest.raises(ValueError):
+ with pytest.raises(MergeError):
  merge(left_w_dups, right, on='a', validate='one_to_one')
 
  # Dups on both
  merge(left_w_dups, right_w_dups, on='a', validate='many_to_many')
 
- with pytest.raises(ValueError):
+ with pytest.raises(MergeError):
  merge(left_w_dups, right_w_dups, left_index=True,
  right_index=True, validate='many_to_one')
 
- with pytest.raises(ValueError):
+ with pytest.raises(MergeError):
  merge(left_w_dups, right_w_dups, on='a',
  validate='one_to_many')
 
@@ -842,7 +842,7 @@ def test_validation(self):
  'um... weasel noise?']},
  index=range(3))
 
- with pytest.raises(ValueError):
+ with pytest.raises(MergeError):
  merge(left, right, on='a', validate='1:1')
 
  result = merge(left, right, on=['a', 'b'], validate='1:1')

pandas/tests/test_errors.py

@@ -10,7 +10,7 @@
  "exc", ['UnsupportedFunctionCall', 'UnsortedIndexError',
  'OutOfBoundsDatetime',
  'ParserError', 'PerformanceWarning', 'DtypeWarning',
- 'EmptyDataError', 'ParserWarning'])
+ 'EmptyDataError', 'ParserWarning', 'MergeError'])
 def test_exception_importable(exc):
  from pandas import errors
  e = getattr(errors, exc)