Fix merge() method to return MicroDataFrame

CLAUDE.md

@@ -2,7 +2,9 @@
 
 ## Code Style
 - All files must end with a newline character
-- Run `make lint` before committing to catch style issues
+- **ALWAYS run `make format` before committing** - this will auto-fix most style issues
+- Run `make lint` after formatting to check if there are any remaining issues
+- **IMPORTANT**: `make format` will fail if there are lines over 79 characters that black can't fix (usually in strings/comments). You must manually break these lines.
 
 ## Changelog Requirements
 - Every PR must include a `changelog_entry.yaml` file at the root
@@ -16,8 +18,14 @@
 - The file must not be empty and must end with a newline
 
 ## Testing
-- Run tests with: `python3 -m pytest microdf/tests/ -v`
+- Install development dependencies first: `make install` or `pip install -e ".[dev]"`
+- Run all tests: `make test` or `pytest -q --cov=microdf --cov-report=xml`
+- Run specific test: `python3 -m pytest microdf/tests/test_microseries_dataframe.py::test_df_init -v`
 - Ensure all tests pass before creating a PR
+- If tests fail, check for:
+  - Missing `_link_all_weights()` calls after setting weights
+  - Proper handling of both array and string arguments in `set_weights()`
+  - Deprecation warnings properly configured with `stacklevel=2`
 
 ## Pull Request Process
 1. Create a feature branch from master
@@ -33,4 +41,27 @@
 
 ## Documentation
 - Documentation notebooks are in `docs/` directory
-- When removing functionality, consider impact on documentation examples
+- When removing functionality, consider impact on documentation examples
+
+## Common CI Failures and Solutions
+
+### Test Failures
+1. **set_weights() with string not working**: Ensure `_link_all_weights()` is called for both string and array cases
+2. **Deprecation warnings in tests**: Import warnings and suppress with `warnings.simplefilter("ignore", DeprecationWarning)` in test setup
+3. **MicroSeries not properly linked**: Check that all DataFrame operations call `_link_all_weights()` after modifying structure
+
+### Linting Failures
+1. **Line length**: Run `make format` to auto-fix most issues
+2. **Import order**: `isort` is configured to work with black, run `make format`
+3. **Docstring formatting**: `docformatter` enforces 79-char wrapping, run `make format`
+4. **File endings**: Ensure all files end with a newline
+
+### Before Pushing
+**CRITICAL: Always run these commands locally before pushing:**
+```bash
+make format  # Auto-fix style issues (ALWAYS RUN THIS FIRST!)
+make lint    # Check for remaining issues (should pass after format)
+make test    # Run all tests
+```
+
+If CI fails with linting errors, it's almost always because `make format` wasn't run.

Makefile

@@ -5,6 +5,13 @@ format:
 	isort --profile black microdf/
 	docformatter --wrap-summaries 79 --wrap-descriptions 79 --in-place --recursive microdf/
 	black . -l 79
+	@echo "Checking for lines that are too long (E501)..."
+	@if flake8 . --select=E501 --max-line-length=79 2>/dev/null | grep -q .; then \
+		echo "WARNING: The following lines are too long and must be manually fixed:"; \
+		flake8 . --select=E501 --max-line-length=79; \
+		echo "Please manually break these long strings/comments to be under 79 characters."; \
+		exit 1; \
+	fi
 
 lint:
 	linecheck .

changelog_entry.yaml

@@ -1,4 +1,13 @@
 - bump: patch
   changes:
-    changed:
-    - Move publishing to pypi to after versioning job.
+    fixed:
+    - MicroDataFrame.merge() now works correctly by implementing inplace support for the drop() method
+    - merge() now returns a MicroDataFrame instead of a regular DataFrame (Fixes #194)
+    - MicroDataFrame aggregation functions now skip non-numeric columns instead of raising errors (Fixes #213)
+    added:
+    - __getattr__ method to MicroDataFrame for intuitive column access via dot notation (Fixes #220)
+    - Full pandas argument support to drop() and merge() methods (Addresses #212)
+    - nullify_weights() method to both MicroDataFrame and MicroSeries to set all weights to 1 (Fixes #176)
+    - Test coverage for set_weights() with string column name argument
+    deprecated:
+    - set_weight_col() method - use set_weights() with a string argument instead (Fixes #208)