The codes gets the input file from the command line in line 58:

    path = sys.argv[1]

the tmp variable just defines the name for a temporary file that is written during the process, ad erased in the end.

#!/usr/bin/env python3

-- coding: utf-8 --

helpDoc = '''
Add Page Number to PDF file with Python
Python 给 PDF 添加 页码
usage:
python addPageNumberToPDF.py [PDF path]
require:
pip install reportlab pypdf2
Support both Python2/3, But more recommend Python3

tips:
* output file will save at pdfWithNumbers/[PDF path]_page.pdf
* only support A4 size PDF
* tested on Python2/Python3@ubuntu
* more large size of PDF require more RAM
* if segmentation fault, plaese try use Python 3
* if generate PDF document is damaged, plaese try use Python 3

Author:
Lei Yang ([email protected])

GitHub:
https://gist.github.com/DIYer22/b9ede6b5b96109788a47973649645c1f
'''
print(helpDoc)

import reportlab
from reportlab.lib.units import mm
from reportlab.pdfgen import canvas

from PyPDF2 import PdfWriter, PdfReader

def createPagePdf(num, tmp):
c = canvas.Canvas(tmp)
for i in range(1,num+1):
c.drawString((210//2)*mm, (4)*mm, str(i))
c.showPage()
c.save()
with open(tmp, 'rb') as f:
pdf = PdfReader(f)
layer = pdf.pages[0]
return layer

if name == "main":
pass
import sys,os
path = 'MLDS17f.pdf'
if len(sys.argv) == 1:
if not os.path.isfile(path):
sys.exit(1)
else:
path = sys.argv[1]
base = os.path.basename(path)

tmp = "__tmp.pdf"

batch = 10
batch = 0
output = PdfWriter()
with open(path, 'rb') as f:
    pdf = PdfReader(f)
    n = len(pdf.pages)
    if batch == 0:
        batch = -n
    createPagePdf(n,tmp)
    if not os.path.isdir('pdfWithNumbers/'):
        os.mkdir('pdfWithNumbers/')
    with open(tmp, 'rb') as ftmp:
        numberPdf = PdfReader(ftmp)
        for p in range(n):
            if not p%batch and p:
                newpath = path.replace(base, 'pdfWithNumbers/'+ base[:-4] + '_page_%d'%(p//batch) + path[-4:])
                with open(newpath, 'wb') as f:
                    output.write(f)
                output = PdfWriter()
            print('page: %d of %d'%(p, n))
            page = pdf.pages[p]
            numberLayer = numberPdf.pages[p]

            page.merge_page(numberLayer)
            output.add_page(page)
        if output._pages:
            newpath = path.replace(base, 'pdfWithNumbers/' + base[:-4] + '_page_%d'%(p//batch + 1)  + path[-4:])
            with open(newpath, 'wb') as f:
                output.write(f)

    os.remove(tmp)