ValueError: incomplete format

I’m trying to take two PDF documents, remove the first page from doc1 and add page 1 from doc2. I think I have the code mostly where it needs to be, but I’m receiving “ValueError: incomplete format.” Here is the code I have, and the error it’s giving me is for the third to last line.

import os, shutil, sys, PyPDF2
from PyPDF2 import PdfFileWriter, PdfFileReader

origList = list()
for root, dirs, files in os.walk(r'C:UsersUser1Desktoppytestorig'):
    for file in files:
            origList.append(file)
print "Original PDF list:"
print origList

stampList = list()
for root, dirs, files in os.walk(r'C:UsersUser1Desktoppyteststamp'):
    for file in files:
            stampList.append(file)
print "Stamped PDF List:"
print stampList

oX = 0
output = PdfFileWriter()
for document in origList:
    file1 = PdfFileReader(open(r'C:UsersUser1Desktoppytestorig%s' %origList[oX], "rb"))
    file2 = PdfFileReader(open(r'C:UsersUser1Desktoppyteststamp%s' %stampList[oX], "rb"))
    file1.decrypt("")
    curFile = origList[oX]
    output.addPage(file2.getPage(0))
    file2Pages = file2.getNumPages()
    file2Counter = 1
    while file2Counter <= file2Pages:
        output.addPage(file1.getPage(file2Counter))
        file2Counter = file2Counter + 1
    outputStream = file(r'C:UsersUser1Desktoppytestoutput%' %curFile, "wb")
    output.write(outputStream)
    oX = oX + 1

The line the error is for is:

outputStream = file(r'C:UsersUser1Desktoppytestoutput%' %curFile, "wb")

I followed the examples given with the module, and I thought that was how it should be written.