You can loop through the Series with apply()
function and convert each list to a Series
, this automatically expand the list as a series in the column direction:
df[0].apply(pd.Series)
# 0 1 2
#0 8 10 12
#1 7 9 11
Update: To keep other columns of the data frame, you can concatenate the result with the columns you want to keep:
pd.concat([df[0].apply(pd.Series), df[1]], axis = 1)
# 0 1 2 1
#0 8 10 12 A
#1 7 9 11 B