Safety Warning (Dry Runs and Backups)

diagram the dry-run pattern, and why it is not optional for a bulk script mermaid

  flowchart TD
  A["build the list of planned actions"] --> B["print every one"]
  B --> C{"--apply passed?"}
  C -->|no, the default| D["stop here -- nothing was changed"]
  C -->|yes| E{"is there a backup?"}
  E -->|no| F["make one first"]
  E -->|yes| G["perform the actions"]
  F --> G
  G --> H["log what was actually done, not what was planned"]
  D --> I["read the output, then re-run with --apply"]

A script that renames or deletes across a directory tree has no undo. The shape that makes it safe is a single flag threaded to one place: the code decides what it would do, prints it, and only acts when told to. The default should be the harmless one, so a script run by accident does nothing.

Why this matters

Automation can:

• delete thousands of files instantly
• overwrite important documents
• send emails/messages to the wrong people

You want guardrails.

Dry run pattern

A dry run prints what would happen without doing it.

dry_run_pattern.py

from pathlib import Path
 
 
def delete_tmp_files(folder: Path, dry_run: bool = True):
    for path in folder.rglob("*.tmp"):
        if dry_run:
            print("[DRY RUN] would delete", path)
        else:
            print("deleting", path)
            path.unlink()
 
 
delete_tmp_files(Path("./demo"), dry_run=True)

Use a sandbox folder

• Copy a small sample dataset
• Run scripts there first

Always keep backups

At minimum:

• zip the folder before modifying it
• store backups outside the working directory

Add logging (not print)

basic_logging.py

import logging
 
logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s %(levelname)s %(message)s"
)
 
logging.info("starting job")

Add confirmations for destructive actions

confirm_delete.py

from pathlib import Path
 
folder = Path("./demo")
ans = input(f"Really delete all .tmp files under {folder}? (yes/no) ")
if ans.strip().lower() != "yes":
    raise SystemExit("Cancelled")