PDF is not saving in locally in flask server

It won’t work if you just copy your script into a Flask application. Adjust your code to the circumstances and it will work.

You should be concerned with the line if __name__ == '__main__': . This makes no sense within your route. Read here to get more information.

The example below uses Flask’s async extra and should meet your needs.

The user can search for publications by entering a title. If he then selects one, the possible chapters are offered as a PDF for download. If a chapter is selected for download, the processing essentially corresponds to your specifications. A temporary directory is created into which the available images are downloaded. You have two alternatives to choose from, depending on where and how you want to create the directory. Once all images have been loaded, a PDF is generated based on their path information, which is delivered directly from memory. The directory used is then deleted.

Flask

from PIL import Image
from flask import (
    Flask, 
    abort, 
    render_template, 
    request, 
    send_file
)
from fpdf import FPDF
from functools import partial
from io import BytesIO
from kissmanga import (
    get_search_results, 
    get_manga_details, 
    get_manga_episode, 
    get_manga_chapter
)

import asyncio
import aiohttp
import aiofiles
import os
import shutil
import tempfile
import urllib
import uuid

app = Flask(__name__)

@app.route('/')
def index():
    title = request.args.get('qs')
    results = []
    if title:
        results = get_search_results(query=title)
        if 'status' in results:
            results = []
    return render_template('index.html', **locals())

@app.route('/episode/<mangaid>')
def episode(mangaid):
    try:
        episode = get_manga_episode(mangaid=mangaid)
        return render_template('episode.html', **locals())
    except Exception as exc:
        abort(404)

@app.route('/chapter/<mangaid>/<int:num>')
async def chapter(mangaid, num):
    chapter = get_manga_chapter(mangaid=mangaid, chapNumber=num)
    if chapter == 'Invalid Mangaid or chapter number':
        abort(404)

    # Either manage a folder manually ... 
    # try:
    #   urls = eval(chapter['totalPages'])
    #   dest = os.path.join(app.instance_path, 'downloads', str(uuid.uuid4()))
    #   try:
    #       os.makedirs(dest)
    #   except: pass
    #   filenames = await download_chapter(mangaid, num, urls, dest)
    #   buffer = BytesIO(gen_pdf(filenames).encode('latin-1'))
    #   return send_file(
    #       buffer, 
    #       mimetype='application/pdf', 
    #       download_name=f'{mangaid}_{num}'
    #   )
    # except Exception as exc:
    #   app.logger.exception(exc)
    #   abort(500)
    # finally:
    #   shutil.rmtree(dest)

    # ... or use a temporary folder.
    with tempfile.TemporaryDirectory() as dest:
        try:
            urls = eval(chapter['totalPages'])
            filenames = await download_chapter(mangaid, num, urls, dest)
            buffer = BytesIO(gen_pdf(filenames).encode('latin-1'))
        except Exception as exc:
            app.logger.exception(exc)
            abort(500)

        return send_file(
            buffer, 
            mimetype='application/pdf', 
            download_name=f'{mangaid}_{num}'
        )

async def download_chapter(mangaid, chapter, urls, dest):
    def _url2path(url, root, size):
        _path = urllib.parse.urlparse(url).path
        _path, _name = os.path.split(_path)
        _root, _ext = os.path.splitext(_name)
        return url, os.path.join(root, f"{_root.rjust(size, '0')}{_ext}")
    async with aiohttp.ClientSession() as session:
        size = len(str(len(urls)))
        tasks = [
            fetch(session, _url, _path) 
            for _url, _path in map(partial(_url2path, root=dest, size=size), urls)
        ]
        return await asyncio.gather(*tasks)

async def fetch(session, url, filename):
    try:
        async with session.get(url) as response:
            assert response.status == 200
            async with aiofiles.open(filename, mode='wb') as fp:
                await fp.write(await response.read())
            return filename
    except Exception as exc:
        return None

def gen_pdf(filenames):
    pdf = FPDF() 
    for filename in filenames:
        if not filename: continue
        cover = Image.open(filename)
        width, height = cover.size
        if width < height: 
            pdf.add_page(orientation='P')
            pdf.image(
                filename, 
                0, 0, 
                max(210, min(210, width)), 
                max(297, min(297, height))
            )
        else:
            pdf.add_page(orientation='L')
            pdf.image(
                filename, 
                0, 0, 
                max(297, min(297, width)), 
                max(210, min(210, height))
            )
    return pdf.output(dest='S')

HTML (./templates/index.html)

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Index</title>
</head>
<body>
    <form>
        <input type="text" name="qs" autocomplete="off" spellcheck="false" value="{{ title or '' }}" />
        <input type="submit" value="Go" />
    </form>

    <div>
        {% if results -%}
        <ul>
            {% for item in results -%}
            <li><a href="{{ url_for('episode', mangaid=item.mangaid) }}">{{ item.title }}</a></li>
            {% endfor -%}
        </ul>
        {% else -%}
        <p>No results found</p>
        {% endif -%}
    </div>
</body>
</html>

HTML (./templates/episode.html)

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>Episode</title>
</head>
<body>
    <h1>{{ episode.title }}</h1>
    <ul>
    {% for i in range(1, episode.totalchapter | int + 1) -%}
    <li><a href="{{ url_for('chapter', mangaid=mangaid, num=i) }}">Chapter {{ i }}</a></li>
    {% endfor -%}
    </ul>
</body>
</html>