safe-file-writing

# Safe File Writing ## ⚠️ Never Use write_file for Large Files When editing or overwriting scripts >400 lines, **always use `patch` instead of `write_file`**. `write_file` truncates long content silently, producing corrupt but compilable-looking files. ## Safe Editing Patterns ### Pattern 1: Patch Only (Preferred) ```bash # Only modify the exact lines you need to change patch --path scripts/weekly_report.py \ --old "old line" \ --new "new line" ``` ### Pattern 2: Import and Run When you need to generate output without risking the source file: ```python # Create a small wrapper script import sys sys.path.insert(0, 'scripts') from weekly_report import * # Use existing functions directly build_excel(wk_m, mo_m, fb_agg, wt, mt, 'output.xlsx') ``` ### Pattern 3: Backup First If you absolutely must rewrite: 1. Copy original first 2. Write new content 3. Verify compilation before deleting backup ## Excel File Locks `.xlsx` files locked by Excel → openpyxl raises PermissionError. **Fix:** Write to a new filename like `xxx_v19_new.xlsx`, never overwrite the open file.