ENH: Add merge type validation on pandas.merge

[KevsterAmp]

• closes BUG: UnboundLocalError when full outer merging two dataframes #59422 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature

Tests on pandas.merge

(pandas-dev) kev@mac pandas % pytest pandas/tests/reshape/merge/test_merge.py + /opt/homebrew/Caskroom/miniforge/base/envs/pandas-dev/bin/ninja [1/1] Generating write_version_file with a custom command ============================================================================================================ test session starts ============================================================================================================= platform darwin -- Python 3.10.14, pytest-8.3.2, pluggy-1.5.0 PyQt5 5.15.9 -- Qt runtime 5.15.8 -- Qt compiled 5.15.8 rootdir: /Users/kev/self/pandas configfile: pyproject.toml plugins: localserver-0.0.0, qt-4.4.0, cov-5.0.0, anyio-4.4.0, hypothesis-6.108.7, cython-0.3.1, xdist-3.6.1 collected 939 items pandas/tests/reshape/merge/test_merge.py ........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... ------------------------------------------------------------------------------------------ generated xml file: /Users/kev/self/pandas/test-data.xml ------------------------------------------------------------------------------------------ ============================================================================================================ slowest 30 durations ============================================================================================================ 0.02s call pandas/tests/reshape/merge/test_merge.py::TestMergeDtypes::test_merge_ea_with_string[inner-str0] 0.02s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_merge_non_unique_indexes 0.01s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_validation 0.01s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_merge_indicator_result_integrity 0.01s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_indicator 0.01s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_merge_non_unique_index_many_to_many 0.01s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_merge_left_empty_right_notempty (23 durations < 0.005s hidden. Use -vv to show these durations.) ============================================================================================================ 939 passed in 1.37s ============================================================================================================= 

Error Reproducible Example

from datetime import datetime data_A = list() data_B = list() for i in range(10): data_A.append({ "id": i, "created_date": datetime.today(), "created_at": datetime.now(), }) data_B.append({ "id": i if i % 2 == 0 else 3*i, "created_date": datetime.today(), "created_at": datetime.now(), }) df_A = pd.DataFrame.from_dict(data_A) df_B = pd.DataFrame.from_dict(data_B) df_A.merge(df_B, how="full", on="id")

Traceback (most recent call last): File "/Users/kev/self/pandas/test.py", line 29, in <module> df_A.merge(df_B, how="full", on="id") File "/Users/kev/self/pandas/pandas/core/frame.py", line 10807, in merge return merge( File "/Users/kev/self/pandas/pandas/core/reshape/merge.py", line 355, in merge raise ValueError(f"'{how}' is not a valid Merge type ({merge_type})") ValueError: 'full' is not a valid Merge type (['left', 'right', 'inner', 'outer', 'cross']) 

Not sure if it should raise ValueError or MergeError

[mroeschke]

This should probably be in _MergeOperation.

And a test is needed

[KevsterAmp]

@mroeschke - moved it to _MergeOperation and added asof as valid Merge Type.


Added test function to validate it as well. Thanks

[KevsterAmp]

@mroeschke - Added tests and added asof as valid merge type, running pytest pandas/tests/reshape/merge passes all tests.

(pandas-dev) kev@mac pandas % pytest pandas/tests/reshape/merge + /opt/homebrew/Caskroom/miniforge/base/envs/pandas-dev/bin/ninja [4/4] Linking target pandas/_libs/tslibs/offsets.cpython-310-darwin.so ============================================================================================================ test session starts ============================================================================================================= platform darwin -- Python 3.10.14, pytest-8.3.2, pluggy-1.5.0 PyQt5 5.15.9 -- Qt runtime 5.15.8 -- Qt compiled 5.15.8 rootdir: /Users/kev/self/pandas configfile: pyproject.toml plugins: localserver-0.0.0, qt-4.4.0, cov-5.0.0, anyio-4.4.0, hypothesis-6.108.7, cython-0.3.1, xdist-3.6.1 collected 1332 items pandas/tests/reshape/merge/test_join.py .......................................................................... pandas/tests/reshape/merge/test_merge.py ................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................. pandas/tests/reshape/merge/test_merge_asof.py .s...................................................................................................s.....................s............................. pandas/tests/reshape/merge/test_merge_cross.py ................. pandas/tests/reshape/merge/test_merge_index_as_string.py ................................................................................ pandas/tests/reshape/merge/test_merge_ordered.py ..................... pandas/tests/reshape/merge/test_multi.py .......................................... ------------------------------------------------------------------------------------------ generated xml file: /Users/kev/self/pandas/test-data.xml ------------------------------------------------------------------------------------------ ============================================================================================================ slowest 30 durations ============================================================================================================ 0.02s call pandas/tests/reshape/merge/test_join.py::TestJoin::test_full_outer_join 0.02s call pandas/tests/reshape/merge/test_join.py::test_join_multiindex_not_alphabetical_categorical[categories0-values0] 0.02s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_merge_non_unique_indexes 0.02s call pandas/tests/reshape/merge/test_multi.py::TestMergeMulti::test_compress_group_combinations 0.02s call pandas/tests/reshape/merge/test_join.py::TestJoin::test_right_outer_join 0.01s call pandas/tests/reshape/merge/test_multi.py::TestMergeMulti::test_left_join_multi_index[True-True] 0.01s call pandas/tests/reshape/merge/test_multi.py::TestMergeMulti::test_left_join_multi_index[False-True] 0.01s call pandas/tests/reshape/merge/test_join.py::TestJoin::test_left_outer_join 0.01s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_validation 0.01s call pandas/tests/reshape/merge/test_join.py::TestJoin::test_join_many_non_unique_index 0.01s setup pandas/tests/reshape/merge/test_merge_index_as_string.py::test_merge_indexes_and_columns_lefton_righton[left_df2-right_df1-left_on3-right_on3-outer] 0.01s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_merge_indicator_result_integrity 0.01s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_indicator 0.01s call pandas/tests/reshape/merge/test_multi.py::TestMergeMulti::test_left_join_multi_index[True-False] 0.01s call pandas/tests/reshape/merge/test_join.py::TestJoin::test_inner_join 0.01s setup pandas/tests/reshape/merge/test_merge_index_as_string.py::test_merge_indexes_and_columns_lefton_righton[left_df2-right_df2-left_on1-right_on1-right] 0.01s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_merge_non_unique_index_many_to_many 0.01s call pandas/tests/reshape/merge/test_merge.py::TestMerge::test_merge_left_empty_right_notempty 0.01s call pandas/tests/reshape/merge/test_multi.py::TestMergeMulti::test_left_join_multi_index[False-False] 0.01s call pandas/tests/reshape/merge/test_join.py::TestJoin::test_join_multiindex (10 durations < 0.005s hidden. Use -vv to show these durations.) ====================================================================================================== 1329 passed, 3 skipped in 2.28s ======================================================================================================= 

[mroeschke]

Please view the CI logs as another test needs fixing https://github.com/pandas-dev/pandas/actions/runs/10337314281/job/28614031854?pr=59435

[mroeschke]

pre-commit.ci autofix

[mroeschke]

Thanks @KevsterAmp