config.ini

[DEFAULT]
basedir = gamefiles/%(appid)s
info_file = %(basedir)s/%(gamedir)s/steam.inf

[Team Fortress 2]
gamedir = tf
appid = 232250
files = server_srv.so
        engine_srv.so
        server.dll
        engine.dll
        steam.inf
command = cmd /C echo bepis

[Counter Strike: Global Offensive]
gamedir = csgo
appid = 740
files = server.so
        engine.so
        server.dll
        engine.dll
        steam.inf

main.py

#!/usr/bin/python3

import configparser
import itertools
import json
import os
import pathlib
import shlex
import shutil
import string
import subprocess
import urllib.request

# This requires a version of steam[client] newer than 1.2.0
# current version on pypi is unable to access dedicated server files (e.g. depotid 232250)
# make sure pip / wheel are both updated from their default versions in venv
import steam
import steam.client
import steam.client.cdn
import steam.webapi

def read_steam_inf(steam_info):
	if os.path.exists(steam_info):
		with open(steam_info, 'rt') as c:
			return dict(line.strip().split('=', maxsplit = 1) for line in c.readlines())
	return {}

if __name__ == "__main__":
	config = configparser.ConfigParser(converters = {
		'path': pathlib.Path,
		'lines': lambda x: x.splitlines(),
		'template': string.Template
	})
	config.read('config.ini', encoding = 'utf8')
	
	webapi_client = steam.webapi.WebAPI(key = None)
	
	for section, proxy in config.items():
		if section == configparser.DEFAULTSECT:
			continue
		entries = read_steam_inf(proxy.get('info_file'))
		
		if entries:
			result = webapi_client.ISteamApps.UpToDateCheck(
				appid = entries.get('appID'),
				version = entries.get('PatchVersion')
			)
			
			if result.get('response', {}).get('up_to_date', False):
				continue
		
		steamclient = steam.client.SteamClient()
		steamclient.anonymous_login()

		cdnclient = steam.client.cdn.CDNClient(steamclient)

		download_files = proxy.getlines('files')

		for bin in itertools.chain.from_iterable(
			cdnclient.iter_files(proxy.getint('appid'), filt)
			for filt in [ '*.so', '*.dll', '*.inf' ]
		):
			bin_path = pathlib.Path(bin.filename)
			
			if any(bin_path.name == f for f in download_files):
				target = proxy.getpath('basedir') / bin_path
				target.parent.mkdir(parents = True, exist_ok = True)
				with target.open('wb') as dst:
					shutil.copyfileobj(bin, dst)

		steamclient.logout()

		# run command specified if we've updated
		postupdate_cmd = proxy.gettemplate("command")
		if postupdate_cmd:
			command_args = shlex.split(postupdate_cmd.substitute(dict()))
			subprocess.run(command_args)