safe-file-writing

name	safe-file-writing
description	Safe ways to edit/overwrite files in Hermes Agent. Avoids file corruption from write_file on large files and Excel file locks.
tags	["file","write","patch","safe-editing"]

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)

# 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:

# 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.