Series.ftype Return if the data is sparse|dense.
Deprecated since version 0.25.0: Use dtype() instead.
© 2008–2012, AQR Capital Management, LLC, Lambda Foundry, Inc. and PyData Development Team
Licensed under the 3-clause BSD License.
https://pandas.pydata.org/pandas-docs/version/0.25.0/reference/api/pandas.Series.ftype.html