Need to set default value of widget based on another widget in databricks

metro_choices = [str(metro_df.select('METRO').distinct().collect()[i][0]) 
                 for i in range(len(metro_df.select('METRO').distinct().collect()))]
metro_choices.extend(['All'])

dbutils.widgets.dropdown(name = 'METRO', defaultValue='All', choices = metro_choices, label = 'Select Metro')

if (region == dbutils.widgets.get('REGION') and metro == 'All' and zone == 'All'):
    display(mainDF.filter(col('REGION').isin(region)))
elif (metro == dbutils.widgets.get('METRO') and zone == 'All'):
    display(mainDF.filter(col('REGION').isin(region) & col('METRO').isin(metro)))
else :
    display(mainDF.filter(col('REGION').isin(region) & col('METRO').isin(metro) & col('ZONE').isin(zone)))

initially if i run the dashboard for selected region say 'WEST' it runs fine and even i can select related metro and zone. But if I change region to say 'NORTH' I want metro and zone to auto set for 'All'.