how to know index in pandas code example

Example 1: indexing column in pandas

In [8]: age_sex = titanic[["Age", "Sex"]]

In [9]: age_sex.head()
Out[9]: 
    Age     Sex
0  22.0    male
1  38.0  female
2  26.0  female
3  35.0  female
4  35.0    male

Example 2: indexing column in pandas

In [10]: type(titanic[["Age", "Sex"]])
Out[10]: pandas.core.frame.DataFrame