How to fix [Errno 13] Permission denied with openpyxl

Inspired by Automate the Boring Stuff with Python, I am doing just that! Everything seems to be going well until I try to save the workbooks I edit with openpyxl. I get an error only at that point in the code.

Here is the relevant part of the code (before this I use selenium to download the appropriate file):

#Gets list of files from downloads
list_of_files = glob.glob('PATH/TO/DOWNLOADS/*')

#Finds most recently downloaded file
latest_file = max(list_of_files, key=os.path.getctime)

#Gets path to destination for sheet in downloaded spreadsheet
report = r'PATH/TO/DESTINATION'

#Appends r to string of latest_file path so that it can be read
pyxlOpen = r'%s' % latest_file

#Opens recently downloaded file as workbook object
snapshotWB = xl.load_workbook(pyxlOpen)

#Gets only sheet in the spreadsheet and renames it 'Snapshot'
snapSheet = snapshotWB.worksheets[0]
snapSheet.title = 'Snapshot'

#Opens destination workbook as workbook object 
reportWB = xl.load_workbook("report")


#Gets rid of any old Snapshot sheet if it's in there
if 'Snapshot' in reportWB.sheetnames:
    del reportWB['Snapshot']

#And add in the new one!
newSnapSheet = reportWB.create_sheet("Snapshot")
for row in snapSheet:
    for cell in row:
        newSnapSheet[cell.coordinate].value = cell.value

#Saves the workbooks!
snapshotWB.save(filename = 'latest_file')
reportWB.save(filename = "Practice.xlsm")

I tried to just do paths instead of variables just to test it, and that didn't work either. But the paths must be accurate, or else I couldn't create a workbook object out of them--right? I also tried switching the order of my saving lines just to make sure that one of the workbooks wasn't the problem child. They both are.