Answers for "pandas how to save to an existing excel file"

export pandas dataframe as excel

df.to_excel(r'C:UsersRonDesktopFile_Name.xlsx', index = False)

#if you omit the file path (must also omit 'r') and 
#enter only file_name.xlsx, it will save to your default file location,
# that is, where the file you're reading from is located.

save dataframe as excel file

In [6]: titanic.to_excel("titanic.xlsx", sheet_name="passengers", index=False)