Variable Files with Python

I am trying to have a file path like 'C:\Programfiles\file.txt' but i would like to have file.txt be a variable that i can change whenever i need to. I am trying to compare 2 directories then copy files from one to another if they arent already there. i have this code so far.

import os
import shutil
A= set(os.listdir(r"C:\Users\Morpheous\Desktop\Python Test"))
B= set(os.listdir(r"C:\Users\Morpheous\Desktop\Python Test 2"))
if len(A)< len(B):
    C=B-A
    print("File is: %s" %(C))
    shutil.copy2('C:\\Users\\Morpheous\\Desktop\\Python Test 2\\%r'%(C),'C:\\Users\\Morpheous\\Deskt开发者_如何学Goop\\Python Test')

elif len(A) > len(B):
    C=B-A
    print(C)

and i get an error because the variable is inserted into path with {''} around it. How would i go about doing this?

Please use os.path.join to construct paths. Also, you should put the directories in variables for reuse. Furthermore you need to iterate over the difference between the folders (B - A) in order to get each filename that's in the difference set (C is the set of files that have been added!).

Here's the corrected version - tested and working:

import os
import shutil

pathA = r"C:\Users\Morpheous\Desktop\Python Test"
pathB = r"C:\Users\Morpheous\Desktop\Python Test 2"

A = set(os.listdir(pathA))
B = set(os.listdir(pathB))
C = B - A

if len(C):
    print("Difference is: %s" % repr(C))

    for addedFile in C:
        shutil.copy2(os.path.join(pathB, addedFile),
                     os.path.join(pathA, addedFile))
else:
    print("No new files")

you should use a library like filecmp to compare directories/files

>>> import filecmp
>>> import os
>>> dira = os.path.join("/home","dir1")
>>> dirb = os.path.join("/home","dir2")
>>> os.listdir(dira)
['file.jpg', 'file2.txt']
>>> os.listdir(dirb)
['file1.jpg', 'file2.txt']
>>> r=filecmp.dircmp(a,b)
>>> r.right_only  # only in dirb
['file1.jpg']
>>> r.left_only   # only in dira
['file.jpg']

Use %s instead of %r, and C.pop().replace(' ', '\\ ') instead of C, which is a set and not a string (the replace is needed to "escape" every space -- I think). Last but not least, I think you're using shutil.copy2 wrong: see the docs -- it wants two arguments, not one argument with a space separator.

There may well be other bugs lurking in your code (I'm not sure what that 2\\ part is supposed to mean, for example; and you may need a loop, as copy2 does one file at a time and you may have serveral; etc, etc), but these at least are definitely there.