##########
# Rename fonctions for scripting on the fly
#
import os
import math
from pathlib import Path

def is_picture(entry):
    """Return True if DirEntry is a picture"""
    extension = ("jpg","png")
    for ext in extension:
        if entry.name.endswith('.'+ext):
            return True
    return False

def get_pictures(path):
    """Scan directory for pictures return DirEntry list of files"""
    pictures = []
    with os.scandir(path) as it:
        for entry in it:
            if not entry.name.startswith('.') \
                    and entry.is_file(follow_symlinks=False) \
                    and is_picture(entry):
                pictures.append(entry)
    return pictures

def rename(entries, reverse=False):
    """Rename file"""
    entries = sorted(entries, key=lambda entry: entry.name, reverse=reverse)
    digit_length = int(math.log10(len(entries)) + 1)
    renamed = {}
    for i, entry in enumerate(entries):
        renamed[entry] = '{number:0{width}d}{ext}'.format(number=i,width=digit_length,ext=Path(entry.path).suffix)
    for src, dst in renamed.items():
       os.rename(src, dst)

if __name__ == '__main__':
    entries = get_pictures('/home/nicolas/tmp')
    rename(entries, reverse=True)