I made a list a global variable in my python function, but when I print its value outside of the function, it's blank

Question

I currently have a class that defines three functions that extract the date and device name from images in a specified directory. ¹ The function then copies the images to new file directories based on the date and device name. I need to collect these new directories in a list so I can loop through the directories and extract the individual images to process them. I have to process them after they're sorted in order to keep them separated when I send the data I've extracted to Excel. I tried making a list of these directories in the function by appending the directories as they're being created. When printed inside the function, all of the directories show up, however, if I print it outside the function, the list is blank.

I created the list outside of the class and then assigned the list as a global variable inside the function as was suggested here, however, the list still prints blank outside the function.

newpath = []
class imageSorter:
    global newpath
    newpath = []
    def sort:
        for fname in self.images:
            with PIL.Image.open(os.path.join(self.dirname,fname) as img:
                exif=img._getexif()

            ts=self.preprocess_exif(exif[306])
            date=ts.split(' ')[0]
            manuf=self.preprocess_exif(exif[271)]
            device=self.preprocess_exif(exif[272])
            merged=manuf+' '+device
            year =datetime.dateime.strptime(date, '%Y:%m:%d').strftime('%Y')
            month =datetime.dateime.strptime(date, '%Y:%m:%d').strftime('%b')
            date =datetime.dateime.strptime(date, '%Y:%m:%d').strftime('%d')

        if not os.path.isdir(os.path.join(year,month,date)):               
            os.mkdir(os.path.join(merged,year,month,date))

        shutil.copy(os.path.join(self.dirname,fname),os.path.join(merged,year,month,date,fname)))
        newpath.append(os.path.join(merged,year,month,date))

_{1. This code was written by github user cw-somil}

Please post a [mre] that demonstrates the problem. The description you posted is insufficient to diagnose your problem. — Tom Karzes, Mar 16 '23 at 00:31
How do you possibly expect us to help without showing the code?! — John Gordon, Mar 16 '23 at 00:40
Please provide enough code so others can better understand or reproduce the problem. — Community, Mar 16 '23 at 03:55

Ariana DeLuca · Answer 1 · 2023-03-17T11:25:36.800

The problem is were I was assigning the list as a global variable. I needed to assign the list as a global variable within the function like follows:

shutil.copy(os.path.join(self.dirname,fname),os.path.join(merged,year,month,date,fname))
global newpath
newpath.append(os.path.join(merged,year,month,date))

Make sure to initalize newpath as an empty list outside the class. Then, you should be able to print the list with the new directories outside of the function as long as you have already called the function beforehand.

I made a list a global variable in my python function, but when I print its value outside of the function, it's blank

1 Answers1