Stop renaming files by hand — 30 lines of Python that do it for you

Renaming ten files is annoying. Renaming a hundred is a weekend gone.

You do not need a fancy app for this. A short Python script can rename a whole folder in seconds — and you can practice the same loops and paths you use later in machine learning.

This guide uses simple words and small code steps. Copy, run, tweak.

What you will build

A script that:

1. Looks inside a folder
2. Finds files (for example, all .jpg photos)
3. Renames them in a clean pattern: photo_001.jpg, photo_002.jpg, …
4. First prints what it would do (safe mode)
5. Only renames for real when you flip a switch

Before you start

You need Python 3 on your computer. In a terminal, check:

python --version

If that fails, try:

python3 --version

Create a practice folder with a few dummy files so you do not touch important photos yet.

Step 1 — Point at a folder

Python’s pathlib makes file paths easier to read.

from pathlib import Path

folder = Path("my_photos")  # change this to your folder name

print(folder.exists())
print(list(folder.iterdir())[:5])  # peek at a few items

What this means: Path("my_photos") is “the folder called my_photos next to my script.” exists() checks it is real. iterdir() lists what is inside.

Step 2 — Keep only the files you care about

Folders can hold other folders too. We only want files with a certain ending.

from pathlib import Path

folder = Path("my_photos")
files = [
    f for f in folder.iterdir()
    if f.is_file() and f.suffix.lower() == ".jpg"
]

print(len(files), "jpg files found")
for f in files[:5]:
    print(f.name)

In plain English: “Walk the folder. Keep items that are files and end with .jpg.” Change .jpg to .png or .pdf if you need to.

Step 3 — Plan the new names

We number files so they sort nicely: photo_001, photo_002, …

for i, old_path in enumerate(files, start=1):
    new_name = f"photo_{i:03d}{old_path.suffix.lower()}"
    new_path = folder / new_name
    print(f"{old_path.name}  ->  {new_name}")

i:03d means “pad with zeros to 3 digits” (1 → 001). That keeps order in file explorers.

Step 4 — Dry run (always do this first)

Dry run = show the plan, do not change anything yet.

from pathlib import Path

DRY_RUN = True  # keep True until the printout looks right

folder = Path("my_photos")
files = sorted(
    f for f in folder.iterdir()
    if f.is_file() and f.suffix.lower() == ".jpg"
)

for i, old_path in enumerate(files, start=1):
    new_name = f"photo_{i:03d}{old_path.suffix.lower()}"
    new_path = folder / new_name

    if new_path.exists() and new_path != old_path:
        print("SKIP (name already used):", new_name)
        continue

    if DRY_RUN:
        print(f"[dry-run] {old_path.name} -> {new_name}")
    else:
        old_path.rename(new_path)
        print(f"[renamed] {old_path.name} -> {new_name}")

Run it. Read the lines. If something looks wrong, fix the pattern — your files are still safe.

Step 5 — Rename for real

When the dry-run looks good:

DRY_RUN = False

Run the script again. Watch the [renamed] lines.

Full script (copy-paste)

Save as rename_files.py next to your practice folder:

from pathlib import Path

# --- settings you can change ---
FOLDER = Path("my_photos")
EXTENSION = ".jpg"       # e.g. ".png", ".pdf"
PREFIX = "photo"         # becomes photo_001.jpg
DRY_RUN = True           # set False only when ready
# -------------------------------

def main():
    if not FOLDER.exists():
        print("Folder not found:", FOLDER)
        return

    files = sorted(
        f for f in FOLDER.iterdir()
        if f.is_file() and f.suffix.lower() == EXTENSION.lower()
    )

    if not files:
        print("No matching files.")
        return

    for i, old_path in enumerate(files, start=1):
        new_name = f"{PREFIX}_{i:03d}{old_path.suffix.lower()}"
        new_path = FOLDER / new_name

        if new_path.exists() and new_path != old_path:
            print("SKIP (already exists):", new_name)
            continue

        if DRY_RUN:
            print(f"[dry-run] {old_path.name} -> {new_name}")
        else:
            old_path.rename(new_path)
            print(f"[renamed] {old_path.name} -> {new_name}")

    print("Done.", "Dry-run only." if DRY_RUN else "Files updated.")

if __name__ == "__main__":
    main()

Run:

python rename_files.py

Common mistakes (and easy fixes)

What you just practiced

• Paths with pathlib
• Filtering with a list comprehension
• Loops with enumerate
• A safety switch (DRY_RUN)

Those same ideas show up in data folders, dataset cleanup, and ML project layouts.

Next step

Want guided practice with runnable labs? Try a Python path on Sythra — same spirit: small steps, real practice, no fluff.

Start with a junk folder. Flip DRY_RUN only when the printout looks right. That habit will save you forever.