Using Python to execute a command on every file in a folder

Python might be overkill for this.

for file in *; do mencoder -some options "$file"; rm -f "$file" ; done

The rm -f "$file" deletes the files.

The new recommend way in Python3 is to use pathlib:

from pathlib import Path

mydir = Path("path/to/my/dir")
for file in mydir.glob('*.mp4'):
    print(file.name)
    # do your stuff

Instead of *.mp4 you can use any filter, even a recursive one like **/*.mp4. If you want to use more than one extension, you can simply iterate all with * or **/* (recursive) and check every file's extension with file.name.endswith(('.mp4', '.webp', '.avi', '.wmv', '.mov'))

Use os.walk to iterate recursively over directory content:

import os

root_dir = '.'

for directory, subdirectories, files in os.walk(root_dir):
    for file in files:
        print os.path.join(directory, file)

No real difference between os.system and subprocess.call here - unless you have to deal with strangely named files (filenames including spaces, quotation marks and so on). If this is the case, subprocess.call is definitely better, because you don't need to do any shell-quoting on file names. os.system is better when you need to accept any valid shell command, e.g. received from user in the configuration file.

To find all the filenames use os.listdir().

Then you loop over the filenames. Like so:

import os
for filename in os.listdir('dirname'):
     callthecommandhere(blablahbla, filename, foo)

If you prefer subprocess, use subprocess. :-)