Pandas extension arrays

As of pandas 0.24.0, all of pandas’ internal extension arrays (Categorical, Datetime with Timezone, Period, Interval, and Sparse) are now built on top of the ExtensionArray interface. The fundamental problem with is that it serves two purposes:

As we saw above, the “array” backing a Series or Index might not be a NumPy array, it may instead be an extension array (from pandas or a third-party library). Currently, pandas represents string data using Python objects in a NumPy array, which is slow.

Source: pandas-dev.github.io