if the notebook cannot load, please refer to https://nbviewer.org/github/zhefeng687/Effective-Pandas/blob/c227b0063e7f2671cffb9716089b32d22f8b8577/Pandas%20Exercises.ipynb https://nbviewer.org/github/zhefeng687/effective_pandas/blob/96a95c18ac6837d5943f8a06980c8d8ddf370329/course_materials/pandas_practice.ipynb