Python 3: Code is looking for directories that don't exist when it isn't supposed to

I have been working on the following code:

#ZIPPYORACLE USB worm module.
import os, random, stat
#User chosen at random
picked = 0
userchoice = random.choice (os.listdir ("/media/"))
randomdir = random.choice (os.listdir ("/media/" + userchoice))
picked = "/media/" + userchoice + "/" + randomdir
os.chdir (picked)
os.chmod ("usb.txt", stat.S_IWRITE)
with open ("usb.txt", "w") as file:
    print (picked)
    file.write ("Create a new text file!")

It is supposed to upload a file to a random USB drive. The problem is it works only 10% of the time, but 90% of the time gives errors like these:

NotADirectoryError: [Errno 20] Not a directory: '/media/asher/Ubuntu-MATE 20.10 amd64usb.txtusb.txtusb.txtusb.txt'

I have no idea why this is happening, and have been debugging it for an hour now. Do any of you more experienced programmers know what's causing this issue?

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