Method chaining is possible with all Python objects since each object method must return another object that itself will have more methods. It is not necessary for the method to return the same type of object.

Step 2 first uses value_counts to return a Series and then chains the head method to select the first three elements. The final returned object is a Series, which could also have had more methods chained on it.

In step 3, the isnull method creates a boolean Series. Pandas numerically evaluates False/True as 0/1, so the sum method returns the number of missing values.

Each of the three chained methods in step 4 returns a Series. It may not seem intuitive, but the astype method returns an entirely new Series with a different data type