In python, In this part, you should write a for loop, updating the df_users dataframe. Go through each user, and update their zip-code (column name zip), to Safe Harbour specifications:

• If the user is from a zip code for the which the "Geographic Subdivision" is less than equal to 20000, change the zip code to 0
• Otherwise, change the zip code to be only the first 3 numbers of the full zip cide
• Do all this re-writting the zip_code columns of the df_users DataFrame

Hints: This will be several lines of code, looping through the DataFrame, getting each zip code, checking the geographic subdivision with the population in zip_dict, and settig the zip_code accordingly.