Help with passing value

[dullboy]

Here is my code,

#mycode.py
import click
import json
 
def read_config(ctx, param, value):
   d = json.load(value)
 
   #ctx.default_map = d
 
def retFunc(ctx, param, value):
   return value
 
@click.group(invoke_without_command = True)
@click.option('--config', callback=read_config, type=click.File('r'))
@click.option('--ret1', callback=retFunc)
@click.pass_context
def cli(ctx, **kwargs):
   pass
 
def main():
   cli()
    
if __name__ == '__main__':
   main()

The code above will read a json file called "config.json" shown below.

{
  "ret1" : 1
}

Now if I run "mycode.py" as mycode.py --config config.json, value won't be passed to the callback function retFunc. But if I uncomment out the statement ctx.default_map = d in the callback function read_config, then I got the value passed to the function retFunc. Why? Thanks.