virtsizes = {
"type1": { "gb": 1.2, "xxx": 0, "yyy": 30 },
"type2": { "gb": 1.5, "xxx": 2, "yyy": 20 },
"type3": { "gb": 2.3, "xxx": 0.1, "yyy": 10 },
}
d = {k:v['gb'] for k,v in virtsizes.items()}
print (d)
{'type2': 1.5, 'type1': 1.2, 'type3': 2.3}
df = pd.DataFrame({'vol-type':['type1','type2']})
df["real_size"] = df["vol-type"].map(d)
print (df)
vol-type real_size
0 type1 1.2
1 type2 1.5