yh.py

price = {
    'A006340': {
        'daygap_list' : [0.025, 0.041, 0.037],
        'geo_mean': 0.01
    },

    'A001324': {
        'daygap_list': [0.01, 0.023, 0.012],
        'geo_mean': 0.008
    }
}

li = []
for code in price.keys():
    li.append({'code': code, 'mean': price[code]['geo_mean']})

sorted_li = sorted(li, key=(lambda x: x['mean']), reverse=True)

# 좀더 한 줄에 복잡하게 하는 방법
sorted_li2 = sorted(price.keys(), key=(lambda x: price[x]['geo_mean']), reverse=True)
print(sorted_li)
print(sorted_li2)