How to download a config file in custom component?

I am building a media player integration for my SFR stb in visual studio code.

in my config folder there is a file with my sources:

'{"TF1": "1", "France 2": "2","France 3": "3"...}'

how to define a file in with the sources.json content ?

source_list = '{"TF1": "1", "France 2": "2","France 3": "3"...}'

I made a little progress
I found how to access my file
for example in the setup_platform function this works:

from homeassistant.util.json import load_json
config_path = hass.config.path("sources.json")
source_list = load_json(config_path)

but not return a string (it’s normal)
How to make source_list a string
I tried

with open(config_path) as f:
    source_list = f.readlines()

Reports a error

config_path = hass.config.path("sources.json")
with open(config_path, encoding="utf8") as f:
   source_list =