Flask - PyPDF2 - Exporting in memory pdf file - flask

Question

I'm trying to export a pdf file from a flask app but for some reason I can't seem to write it correctly.
It does work when I'm exporting to my local folder but I get a blank pdf when exporting through Flask.
Any ideas ?
pdf = PdfFileWriter()
p1 = PdfFileReader(open(os.path.join(STATICDIR,'page1.pdf'), "rb"))
p2 = PdfFileReader(open(os.path.join(STATICDIR,'page2.pdf'), "rb"))
p3 = PdfFileReader(open(os.path.join(STATICDIR,'lastpage.pdf'), "rb"))
pdf.addPage(p1.getPage(0))
pdf.addPage(p2.getPage(0))
pdf.addPage(p3.getPage(0))
#this works
#outputStream = open(r"output.pdf", "wb")
#pdf.write(outputStream)
outfile = BytesIO()
pdf.write(outfile)
return Response(pdf, mimetype='application/pdf',
headers={'Content-Disposition': 'attachment;filename=output.pdf'})

Answer 1

BytesIO is just a buffer containing some data it isn't associated with any real file on the disk, It's just a chunk of memory that behaves like a file. You first need to write the contents of PdfFileWriter() to the buffer then write the values of the buffer to the pdf file. Flask has a neat function send_file which allows you to send the contents of a file to the client.
from pypdf2 import PdfFileWriter
from flask import send_file
pdf = PdfFileWriter()
p1 = PdfFileReader(open(os.path.join(STATICDIR,'page1.pdf'), "rb"))
p2 = PdfFileReader(open(os.path.join(STATICDIR,'page2.pdf'), "rb"))
p3 = PdfFileReader(open(os.path.join(STATICDIR,'lastpage.pdf'), "rb"))
pdf.addPage(p1.getPage(0))
pdf.addPage(p2.getPage(0))
pdf.addPage(p3.getPage(0))
#this works
outputStream = open(r"output.pdf", "wb")
pdf.write(outputStream)
outfile = BytesIO()
pdf.write(outfile)
with open("output.pdf", "wb") as f:
f.write(outfile.getvalue())
return send_file('./output.pdf', mimetype='application/pdf')

Answer 2

Here is the clean code thanks to #darth baba.
I've also added a pptx export that works with this method :
#
#1. PDF EXPORT
#
from pypdf2 import PdfFileWriter
from flask import send_file
pdf = PdfFileWriter()
p1 = PdfFileReader(open(os.path.join(STATICDIR,'page1.pdf'), "rb"))
p2 = PdfFileReader(open(os.path.join(STATICDIR,'page2.pdf'), "rb"))
p3 = PdfFileReader(open(os.path.join(STATICDIR,'lastpage.pdf'), "rb"))
pdf.addPage(p1.getPage(0))
pdf.addPage(p2.getPage(0))
pdf.addPage(p3.getPage(0))
#this works
outputStream = open(r"output.pdf", "wb")
pdf.write(outputStream)
outfile = BytesIO()
pdf.write(outfile)
outfile.seek(0)
return send_file(outfile,
mimetype='application/pdf'
attachment_filename='output.pptx')
#
#2. PPTX EXPORT
#
from pptx import Presentation
from flask import send_file
prs = gen.GenPPT(STATICDIR, lst_ath, lst_choice_sous_cat) #creates presentation
outfile = BytesIO()
prs.save(outfile)
outfile.seek(0)
return send_file(outfile,
mimetype="application/vnd.openxmlformats-officedocument.presentationml.presentation",
as_attachment=True,
attachment_filename='output.pptx')