pdf booklet maker by shuffling

pdfbooklet.py

from pyPdf import PdfFileWriter, PdfFileReader
import sys
def generate_page_list(n):
    print n,'pages'
    foo = []
    flag1 = n % 2
    # if n is an odd number, page n+1 is a BlankPage
    if flag1 == 1:
        n += 1
    
    a = 0
    b = n - 1
    
    #4M or 4M+2 ?
    flag2 = n % 4
    if flag2 == 0: # n = 4M
        print 'page type:4M'
        for i in range(n):
            flag = i % 4
            if flag == 0:
                foo.append(b)
                b -= 1
            elif flag == 1 or flag == 2:
                foo.append(a)
                a += 1
            elif flag == 3:
                foo.append(b)
                b -= 1
        if flag1 == 1:
            foo[foo.index(n - 1)] = 'b'
    else: #n = 4M+2
        print 'page type:4M+2'
        for i in range(n + 2):
            flag = i % 4
            if flag == 0 or flag == 3:
                if i == 0 or i == 3:
                    foo.append('b')
                else:
                    foo.append(b)
                    b -= 1
            elif flag == 1 or flag == 2:
                foo.append(a)
                a += 1
        if flag1 == 1:
            foo[foo.index(n - 1)] = 'b'   
    return foo
    

output = PdfFileWriter()
try:
    pdf = PdfFileReader(file(sys.argv[1], "rb"))
except:
    print 'No input file'
    print 'Usage:',sys.argv[0],'[input file]'
    sys.exit(1)
print 'proceeding..'

lastpage = pdf.getPage(0)
width = lastpage.mediaBox.getWidth()
height = lastpage.mediaBox.getHeight()

for i in generate_page_list(pdf.getNumPages()):
    if i == 'b':
        output.addBlankPage(width,height)
    else:
        output.addPage(pdf.getPage(i))
        
print 'writing file...'
outputStream = file(sys.argv[1] + '_booklet.pdf', "wb")
output.write(outputStream)
outputStream.close()
print "%s pages created." % output.getNumPages()