Stop Creating New List on Each Iteration - python-3.x

Question

The following code extracts the subtitle data from mkv files. I want the output in one list but it creates a list for each track. How can the code be changed to give one list containing all the tracks rather than a list for each track?
#!/usr/bin/env python3
import os
import re
import json
import subprocess
from itertools import chain
mkvmerge = "/usr/bin/mkvmerge"
keep_lang = "eng"
#############################################################################
def extract_subs(mkv_list):
subtitle_tracks = []
video_tracks = []
audio_tracks = []
extractList = []
for file in mkv_list:
### Commandline auguments for extracting info about the mkv file
command = [mkvmerge, "-i", "-F", "json", file]
# Ask mkvmerge for the json info
process = subprocess.run(command, capture_output=True, text=True, check=True)
stdout = process.stdout
### Process the json response
json__data = json.loads(stdout)
tracks = json__data.get('tracks', [])
### find audio and subtitle tracks
audio = []
subtitle = []
track_list = []
for track in tracks:
track['properties']['id'] = track['id']
if track['type'] == 'audio':
audio.append(track)
elif track['type'] == 'subtitles':
subtitle.append(track)
# filter out files that don't need processing
if len(audio) < 2 and len(subtitle) < 2:
pass
#print("\nNo extracted subs to process.", file)
subtitle_keep = list(filter(lambda a: a ['properties']['language']==keep_lang, subtitle))
for s in subtitle_keep:
track_list.append(f"Track #{s['id']}: " f"{s['properties'].get('language')}" f" - " f"{s['codec']}: " + file)
print (track_list)
output
['Track #2: eng - SubRip/SRT: /home/mp/torrents/test/Belfast (2021)/Belfast (2021).mkv', 'Track #3: eng - SubRip/SRT: /home/mp/torrents/test/Belfast (2021)/Belfast (2021).mkv']
['Track #2: eng - SubRip/SRT: /home/mp/torrents/test/The Rescue (2021)/The Rescue (2021).mkv']
desired output
['Track #2: eng - SubRip/SRT: /home/mp/torrents/test/Belfast (2021)/Belfast (2021).mkv', 'Track #3: eng - SubRip/SRT: /home/mp/torrents/test/Belfast (2021)/Belfast (2021).mkv', 'Track #2: eng - SubRip/SRT: /home/mp/torrents/test/The Rescue (2021)/The Rescue (2021).mkv']

Answer 1

It seems like that your variable track_list has the wrong scope.
Try moving it out of the scope of the for loop.
#!/usr/bin/env python3
import os
import re
import json
import subprocess
from itertools import chain
mkvmerge = "/usr/bin/mkvmerge"
keep_lang = "eng"
#############################################################################
def extract_subs(mkv_list):
subtitle_tracks = []
video_tracks = []
audio_tracks = []
extractList = []
track_list = []
for file in mkv_list:
### Commandline auguments for extracting info about the mkv file
command = [mkvmerge, "-i", "-F", "json", file]
# Ask mkvmerge for the json info
process = subprocess.run(command, capture_output=True, text=True, check=True)
stdout = process.stdout
### Process the json response
json__data = json.loads(stdout)
tracks = json__data.get('tracks', [])
### find audio and subtitle tracks
audio = []
subtitle = []
for track in tracks:
track['properties']['id'] = track['id']
if track['type'] == 'audio':
audio.append(track)
elif track['type'] == 'subtitles':
subtitle.append(track)
# filter out files that don't need processing
if len(audio) < 2 and len(subtitle) < 2:
pass
#print("\nNo extracted subs to process.", file)
subtitle_keep = list(filter(lambda a: a ['properties']['language']==keep_lang, subtitle))
for s in subtitle_keep:
track_list.append(f"Track #{s['id']}: " f"{s['properties'].get('language')}" f" - " f"{s['codec']}: " + file)
print (track_list)